Note: Descriptions are shown in the official language in which they were submitted.
2198178
PL~ASTIC COMBINEI) VACUUM AND HOLDING TANR
BACRGROUND AND SUMlUARY OF THE INVR-~lqON
The '~ACU-FLUSH"(g) toilet system for boats and recre~;on~l
vehicles manllf~ct~lred by Se~l~n~i Terh~olo~y, Inc. of Big Prairie,
Ohio, has for many years effectively provided a v~cllllm system
facilitating fl~ hing of a vacuum toilet and hol~ing of the sewage from
the toilet until there iB a need or opportunity to properly dispose of it.
10 Initially, this system included four main components, a vacuum toilet
connected to a vacuum tank, in turn collnected to a vacuum pump, in
turn connected to a holding tank, such as shown in U.S. patent
4,819,279. The number of components was effectively reduced from
four to three by efficiently combining the vacuum pump with the
vacuum tank, such as shown in U.S. patent 5,408,704 and WO
96/41059 (the disclosures of which are both hereby incorporated by
reference herein). The invention relates to a still further development
of such a toilet system which is particularly suitable for use in boats
and caravans or recreational vehicles, where space is at a ~lell~iulll or
20 where relevant cost factors apply. According to the present invention a
single plastic combined vacuum tank and holding tank is provided.
The tank is unreinforced -- that means, as used in this specific~tion
and claims, that it has no reinforcing elongated fibers, such as glass or
metal fil~ments~ integrally incorporated with the plastic material
25 (although other materials, such as talc or glass powder, may be
utilized). The tank may also directly mount the vacuum pump. This
means that the system has a minimum number of components (two), a ,r
vacuum toilet and a combined vacuum/holding tank and vacuum
2198178
pump, or three if the vacuum pump is disposed distinct from the tank.
While the number of components have been reduced according to the
invention, the function~lity of the system is not qignific~ntly
compromised. Rather only cost saving, space~saving, and oper~tion~
5 advantages ensue.
While it has been known per se to use a combined v~c~ m and
holding tank for sewage systems, the prior art constr~lction~ have
included expensive tank materials and/or have necessarily been
cylindrical (with domed ends), and do not have the low cost or space
0 saving advantages accol.lhlg to the invention. For example U S
Patent 3,663,970 relates to a system in which a fiberglass or fiberglass
reinforced combined vacuum and holding tank is provided, requiring
the use of pressure to expel waste, and because of the materials
utilized is expensive. U S Patent 5,002,592 shows a cylindrical (with
domed ends) metal tank connected to a blower and for also for holding
sewage, while U S Patent 5,214,807 shows a dual wall tank. While all
plastic tanks per se have been known before for vehicle sewage
systems, such as in U S Patent 5,408,704, they were relatively small
(only for vacuum in the 5,408,704 patent), and it was unknown that an
20 all unreinforced (e. g. rotational molded or injection molded) plastic
larger tank was possible, such as a combined vacuum and holding tank
as according to the invention.
It is possible to provide a non-cylindrical (e. g. generally
parallelepiped) combined vacuum and holding tank of subst~nti~lly
25 unreinforced all plastic according to the invention by providing a tank
having convoluted, discontinuous surfaces (e. g. the discontinuities
provided by grooves, rh~nnel.q, or other discontinuities), so that the ,r'
tank has no continuous flat surface area of more than about 2~0
2198178
square cm (80 square inches). The size (interior volume) of the t~nk
according to the invention typically is about 45-65 liters (e. g. about 14
g~llon.~), and normally, although not necess~rily under all
circumstances, the vacuum portion of the tank is about 12 liters or
5 more (e. g. under the minimum vacuum portion sitll~tion the
liquid/sewage portion of the tank is about 43 liters).
Acco~ g to one aspect of the present invention a comhinetl
vacuum and holding tank ~c~emhly is provided comprising the
following components: A subst~ti~lly hollow unreinforced non-
0 cylindrical all plastic tank having first and second (substantially
planar) ends, first and second (subst~ti~lly planar) sides, at least one
pump-mounting surface, first and second outlets, an inlet, an upper
surface, and a bottom. A vacuum pump mounted on the at least one
pump-mounting surface exteriorly of the tank. A downwardly
extending sewage transporting tube disposed within the tank
connected to the first outlet. A gas inlet tube disposed within the tank
and connected to the second outlet, and having a top open end adjacent
(i.e. near) the tank upper surface. And a connection between the
vacuum pump and the second outlet exterior of said tank.
If desired a sensor may be provided for sensing the level of
liquid in the tank, as well as means for precluding operation of the
vacuum pump if the sensed level within the tank becomes closer than
a predetermined amount to the air inlet tube open top end so that a
gas volume is always provided adjacent the upper surface inside the
2~ tank. If provided the means for precluding operation of the vacuum
pump if the sensed level within the tank rises too high ensures that
sewage doesn't pass out the vacuum pump (which is usually capable of
pumping liquid too). For example in typical operation, the tank would
- 2198178
have a waste holding capacity of about 40-45 liters (10 to 11 gallons),
and operate with a minimum of about 12 liters (three gallons) of
vacuum, which is generated to between 20-26 cm (8-10 inches) of
mercury (as is col~v~.t;on~l per se). In response to the sen~in~ of the
5 level of the waste, a relay may be closed or opened to detach the
vacuum pump from its power source so that it can no longer operate
until the liquid level drops, or a controller may be provided to take
inform~tion from the sensor and disable the vacuum pump in any
known m~nner. The sensor too may be any conventional structure,
o such as an optical, sonar (including ultrasound), piezoelectric, fluidic,
or me~h~nic~l sensor. For example a conventional float operated
sensor can be utilized.
Typically a gas ~ h~rge tube is co~nected to the vacuum pump
for discharging gas from the tank, e.g. penetrating an exterior
partition wall of a boat (e.g. boat hull) or caravan or recre?~t.io~l
vehicle (e.g. side panel or bottom) in which the tank is mounted, and a
conduit is typically connected to the first outlet for ~ ch~rging sewage
from the tank. The at least one pump-mounting-surface may comprise
a top surface, and may include a second pump-mounting top surface.
20 In that case an optional sewage fli~rh~rge pump may be mounted on
the second pump-mounting top surface and connected to the first
outlet. A conduit is preferably provided connecting the inlet to at least
one vacuum toilet.
The substantially unreinforced plastic tank may be rotational
25 molded from linear low density polyethylene (with or without
additives), although a wide variety of other plastics may be utilized,
and other manufacturing techniques. Rotational molding is preferred, ;
however, since it is easy and inexpensive and does not require seams
2198178
in the tank (which must be sealed, as is necessary with injection
moltling). If the tank is injection molded (if sales volume jllc*fie.~) a
~,vide variety of pl~Qtics, including ABS, may be used. The convoluted,
continuous construction of the tank surface typically includes
5 reinforcing grooves or ~h~nnel.~ formed in the raised portion, and a
simil~r grooved configuration is desirably provided for all surface of
the tank. Also the first and second outlets are typically on opposite
sides of a vertical plane subst~n~;~lly bi~ect;n~ the tank and
intersecting the first and second ends thereof, and face in opposite
o directions.
A vacuum switch is preferably mounted to the tank for sencing
the level of vacuum in the gas volume. Any convention~l construction
of vacuum switch, or like device, may be utilized, the details of the
vacuum sensing not being signific~nt. Typically the vacuum switch is
calibrated to start operation of the pump if the level of vacuum in the
gas volume is lower than a predetermined amount (e.g. if lower than
about twenty centimeters -- eight inches -- of mercury the vacuum
pump is operated until the gas volume is evacuated to a level of about
twenty five centimeters -- roughly about ten inches -- of mercury). The
20 tank typically maintains a m~imum level of vacuum of about twenty
six cm of mercury.
Typically the bottom of the tank is formed with a slope toward a
sump, and integral plastic legs support the tank on a horizontal
surface so that the sump is the lowest part of the tank. The
25 downwardly extending tube preferably comprises a dip tube having an
end termination cut at an angle, .lefining a generally oval-shaped
opening disposed just above the sump. In this m~nner the general ;
2198178
configuration of the tank bottom and the dip tube configuration are
such as illustrated in WO 96/41059.
Accor~ g to another aspect of the present invention a sewage
h~qnllling ~.~sçmbly is provided for a boat, RV or caravan, plane or train
5 comprising the following components: At least one toilet having a
waste ~ h~rge thererlom. An unreinforced non-cylindrical all pl~st;c
comhine-l vacuum and hol~ling tank including an inlet and first and
second outlets. A conduit connectin~ the tank inlet to the toilet waste
çh~rge. A vacuum pump connected to the second outlet. A gas
o handling conduit from the vacuum pump including an end termination
penetrating the boat, plane, train or recreational vehicle exterior
partition. A sewage handling conduit operatively co~necte~l to the first
outlet and having an end termin~tion penetrating the partition. And,
the tank having a top and a bottom, sewage from the toilet provided in
the bottom, and gas at less than atmospheric pressure provided in the
top (usually, but not necessarily, at all times). The details of the tank,
etc., preferably are as described above, including having an interior
volume of about 45-65 liters, a generally parallelepiped configuration,
and a contoured, discontinuous, convoluted surface which has no
20 continuous flat surface area of more than 200 square centimeters (80
square inches). Also a vacuum relief valve may be provided in the
tank.
It is the primary object of the present invention to provide the
optimum in simplicity and cost effectiveness for the h~n(lling of sewage
25 from one or more vacuum toilets, particularly in association with
boats, recreational vehicles or caravans, planes, trains, and other
vehicles. This and other objects of the invention will become clear ~r
21 98 1 78
-
~ from an inspection of the detailed description of the invention and from
the appended claims.
.
RRT~F DES~;nI~llON OF TRF DRAWING~3
FIGURE 1 is a side srhem~t~c view of a conven~ion~l prior art
VACU-FLUSH~) sewage h~n~ling ~y~l~ for a boat, calavan or RV, or
the like;
FIGURE 2 is a view like that of FIGURE 1 showing the
10 simplified system of WO 96/41059;
~ FIGURE 3 is a view like that of FIGURES 1 and 2 of the still
further simplified system according to the present invent.ion;
FIGURE 4 i-s a top plan view of the tank acco~ lhlg to the
present invention (alone), of the system of FIGURE 3;
FIGURE 5 is a longitudinal view, partly in cross-section and
partly in elevation, taken along lines 5-5 of FIGURE 4;
FIGURE 6 is an end view, partly in cross-section and partly in
elevation, taken generally along lines 6-6 of FIGURE 4;
FIGURE 7 is a view like that of FIGURE 5 only taken along
20 lines 7-7 of FIGURE 4;
FIGURE 8 is a bottom plan view of the tank of FIGURE 4;
FIGURE 9 is an exemplary control schematic for the system of
FIGURE 3;
FIGURE 10 is a side schematic view, with the tank and toilet
25 shown in cross-section, of another exemplary embo-liment of a system
according to the present invention; and
FIGURE 11 is a top perspective detail view of a tank accoldillg ;-
to the invention utilizable in the system of FIGURE 10, and with a
2t9at 78
vacuum switch, vacuum relief valve, pump, and external fittings,
thereon.
DETA~T-~n DESCRIPTION OF T~J~; DRAWING~3
In the convent;on~l VACU-FLUSH~) ~y~le~ as illustrated in
FIGURE 1, at least one vacuum toilet 10 having a waste tli~ch~rge on
the bottom thereof i9 connecte~l by a con~ it 11 (typically a fla~hle
hose) to a vacuum tank 12. A vacuum level of about 20-26 cm (8-10
10 inches) of mercury is m~;nhined in the tank 12 by the vacuum pump
13, a conventional vacuum switch on the tank 12 operating the pump
13 to maintain an a~ o~liate vacuum. When the pump 13 is operated
to replenish the vacuum in the vacuum tank 12, sewage is pumped to
the holding tank 14 via conduit 15. The sewage ult.im~tely is
discharged from the holding tank 14 via conduits 16 perhaps by using
an optional sewage discharge pump 17 which is operated only when
there is a me~h~ni.~m for proper disposal of the sewage. The exterior
partition 18 in FIGURE 1 comprises an exterior partition of a boat,
caravan or recreational vehicle, plane, train, or other vehicle, e.g.
20 simulating the form of boat hull in the actual illustration in FIGURE
1. The exterior partition 18 is penetrated by termination 19 of the
conduit 16 from the tank 14. When the pump 17 is not used the
termination 19 is merely connected up to a pump-out facility at a dock,
campsite, terminal, or the like. Conventional valves are provided to
25 preclude sewage from being ~ ch~rged from the tank 14 into conduit
16 unless there is a motive force appropriate for ~ ch~rging the
sewage to a suitable location. ;-
21 981 78
From the holding tank 14 is a conventional vent 20, which may
have a suitable filter therein such as shown in U.S. patent 5,139,655,
with an end termin~tion 22 of the conduit 20 penetrating the partition
18 to vent odolirelo~ s gases from the holding tank 14 to the
5 atmosphere. Another conventional vent 23 is typically also provided
from the conduit 16, typically penetrating another partition (e.g. boat
deck) of the vehicle in which the toilet 10 is provided.
FIGURE 2 illustrates a system accoi li~lg to WO 96/41059. In
this system components comparable to those in the FIGURE 1
0 embodiment are shown by the same reference numeral. Note that in
this case the vacuum tank 12 and the vacuum pump 13 have been
combined, thus reducing the number of major components by one
compared to the system of FIGURE 1.
FIGURE 3 srhem~tic~lly illustrates a system accolLllg to the
present invention. In FIGURE 3 components comparable to those in
FIGURE 1 are shown by the same reference numeral. Note, however,
that in this embodiment the vent tube 20' is shown slightly di~elel,t in
configuration, and without a filter, although a filter may be provided.
In the system of FIGURE 3 the only two major components are one or
20 more vacuum toilets 10 and the combined vacuum/holding tank 25,
which may mount a vacuum pump (like pump 13).
FIGURE 4 is a top plan view of the tank 25 per se. Note that
the tank 25 has first and second end walls 26, 27 and first and second
side walls 28, 29, the side wall 28 being seen in FIGURE 3. It also
25 includes top surfaces 30 adjacent the side wall 28 with a top pump-
mounting surface 31, and a raised portion 32. On the opposite side of
the tank 25 from the surfaces 30-32 (e.g. on the other side of an ,r
im~gin~ry vertical plane P substantially bisecting the tank 25 and
- 2198178-
intersecting the end walls 26, 27) are the top surfaces 33, with another
pump-mounting top surface 34 therebetween. Also provided is a raised
portion shown generally by lafe~e~,ce numeral 35, which includes an
upper surface 36 with reinforcing grooves 37 formed therein. Also seen
5 in FIGURE 4 are an inlet 38 to the hollow interior of the tank 25, a
first outlet 39, and a second outlet 40. Note that the outlets 39, 40 are
on opposite sides of the plane P and face in opposite directic n~. All of
the components 38-40 plefe~ably are subst~n~;~lly circular in cross-
section and are adapted to be readily connected to various conrl-lits,
10 pumps, or other fluid transmitting elements.
The non-cylindrical tank 25 -- as clearly illustrated-in all of the
drawings -- has a number of irregularities in the surface thereof, which
may be characterized as grooves or channels; that is the surface is
convoluted, discontinuous, and contoured. These irregularities are
provided so that there is no flat continuous surface of the tank 25
which is greater than about two hundred square centimeters (eighty
square inches) in area. This allows the tank 25 to be generally
parallelepiped (having space savings over a cylindrical construction)
and yet be made completely of substantially unreinforced plastic and
20 still function properly. For example the tank 25 may be inexpensively
and easily made by conventional rotational molding techniques from a
wide variety of plastics, or may be blow molded. One particularly
desirable plastic is linear low density polyethylene (with or without
additives), although other plastics may be utilized, such as other
25 polyolefins (e. g. polypropylene or other polyethylenes). Also, where
sales volume justifies it, the tank may be injection molded, such as of
ABS or PVC. Tank 25 is much larger than other all plastic tanks used ;
in association with vehicle toilet systems (such as the vacuum (only)
2198178
tank of U S Patent 5,408,704), typically having a total interior volume
of about 45-65 liters.
As seen in FIGURE 8 the bottom of the tank 25 ~lefel ably
comprises downwardly sloping surfaces 41, 42 which meet at a sump
5 43 in a somewhat central loc~tion in the bottom, and ~I.;rre..~ ribs 44
~lefelably are provided integrally mollle~1 with the tank surface
portions forming the bottom. Integrally formed feet 45, 46 are
preferably provided at the ends 26, 27, respectively, of the tank 25
bottom and support the tank 25 on a substantially horizontal surface
o so that the sump 43 is the bottom-most portion of the tank 25 during
normal use.
FIGURE 7 shows the tank 25 particularly as associated with
the vacuum pump and related components. Connected to the second
inlet 40 is a gas inlet tube shown generally by reference numeral 48.
The gas inlet tube 48 may have almost any suitable configuration; the
configuration specifically illustrated in FIGURE 7 is a generally
horizontally extending component 49 from which a generally vertically
extending component 50 projects upwardly having an open end 51
adjacent the interior of the upper surface 36 of the tank 25 raised
20 portion 35. The opening 51 is preferably placed as close to the highest
interior surface of the tank 25 as possible (e.g. from about .25 to 4.0
cm.), while still allowing ready flow of air and other gas thereinto, in
order to minimi7e the possibility that sewage will splash into or
otherwise enter the open end 51. If splash guards, or the like, are
25 used, the spacing may be further than if not used, and if used in a
system which does not move (as does a boat), the spacing also can be
greater. ~-
- 2198~78
12
Mounted on the surface 34 is a vacuum pump 53 of convent.ion~l
construction (comparable to the pumps- 13 in FIGURES 1 and 2). The
vacuum pump 53 is typically driven by an electric motor 54, although
any suitable convent,ion~i type of vacuum pump drive may be ~ e~l.
5 Any convention~l suitablé connection (a screw connection being
illustrated in the e~ernpl~ry embodiment illustrated in FIGURE 7) 52
may be provided connectin~ the outlet 40 to the vacuum pump 53, aIld
a ~ h~rge con~ it 55 from the vacuum pump 53 is typically
connected to the conduit 20', as illustrated in dotted line in FIGURE 7.
o FIGURE 7 also illustrates the inlet 38 connected to the conduit 11,
also shown in dotted line. It is to be understood that any suitable
conduits may be associated with the components illustrated in
FIGURE 7; for example the inlet conduit co~nected to the inlet 38 may
be such as illustrated in WO 96/41059.
FIGURE 5 is the opposite side cross-sectionaVelev~tion~l view of
the tank assembly including the tank 25. In this case a cor nection 58
of conventional construction (e.g. a screw connection, connected
through the deck discharge 23 if on a boat) is connected to the first
outlet 39 of the tank 25 and a ~ii.$~-h~rge pump 59 is optionally
20 mounted on the surface 31, the pump 59 comparable to the pump 17 in
FIGURES 1 and 2 and operated by a motor 60 (such as an electric
motor). Where the pump 59 is utilized the ~ ch~rge outlet 61
therefrom is connected to the conduit 16, but where the pump 59 is not
utilized any suitable conduit like the conduit 16 is provided connected
25 directly from the outlet 39 (or the deck discharge 23) to the end
termination 19. The end termination 19 may be connected to a
suitable pump-out device at a dock, campsite, or the like. ;;
21 981-78
13
Connected to the first outlet 39 inside the tank 25 is the
downwardly extending tube, such as shown generally at in FIGURE 5.
The tube 63 may have any suitable configuration and that illustrated
in FIGURÉ 5 is only e~empl~ry, although a desirable configuration. In
5 this form the tube 63 might be properly characterized as a dip tube
~-~sembly including dip tube 64 including a tubular portion 65 that i8
subst~nti~lly circular in cross-section and elongated about an a~ns, and
having an open end termin~tio~ 66 cut at an angle to its axis of
elongation and ~lefining a substantially oval-shaped opening which is
o above but spaced from the vacuum tank 25 bottom adjacent the sump
43. In this way the dip tube assembly 63 is preferably subst~nti~lly
identical to that illustrated in WO 96/41059.
The assembly according to the invention also comprises a
conventional vacuum switch 70, which is seen in FIGURES 5 and 6 is
typically mounted on the raised surface 32 of the tank 25, adjacent the
inlet 38. The vacuum switch 70 may comprise any conventional
suitable vacuum switch or like device such as shown in U.S. patent
4,819,279, which senses the vacuum within the gas volume within the
tank 25 and operates the vacuum pump 53 if the level of vacuum falls
20 below a predetermined minimum. As is conventional, the vacuum
switch 70 typically senses when the vacuum level has dropped to about
twenty cm (eight inches) of mercury, and then operates the pump 53
until the level of vacuum is raised to about twenty five cm (about ten
inches) of mercury. The tank 25 typically maintains a m~imum level
25 of vacuum of about twenty six centimeters of mercury.
The assembly according to the invention also comprises a sensor
for sensing the level of liquid (sewage) in the tank 25. Convent;on~l ;
sensors are illustrated schematically at 73 and 74 in FIGURES 6 and
_ 2198178
14
9. In FIGURE 6 the sensors 72, 74 are illustrated as convent,ion~l
float operated sensors, the floats being schem~tically illustrated at 73
and 75. The sensor 72 and associated float 73 comprise a three-
quarters full level in~ic~tor (e.g. operating inrlic~tor light 79 in
5 FIGURE 9), while the sensor 74 and associated float 76 comprise a full
level sensor. VVhile me~h~nic~l sensors 72, 74 are illustrated in
FIGURE 6 it is to be understood that any suitable conv~nhon~l sensor
or sensors, whether optical, sonar, piezoelectric, fluidic, or the like,
may be provided. Note that the levels of sewage for three-quarter full
0 and full are indicated by reference lines 76 and 77 in FIGURE 6.
Typically the full level indicated by line 77 is between about
twenty four - forty four liters (six-eleven gallons), leaving a gas volume
(primarily in the raised portion 35) -- and shown by ~eferellce numeral
80 in FIGURE 7 -- of between about ten and sixteen liters (two and
one-half-four gallons (e.g. 3.0-3.5 gallons)). Once the full level 77 has
been reached -- which is far enough below the open top 51 of the gas
inlet 48 so that it is unlikely sewage could enter the open end 51 --
suitable means are provided for precluding operation of the vacuum
pump 53, so that a gas volume is always provided adjacent the upper
20 surface 36 inside the tank 25. Such means are schematically
illustrated at 81 in FIGURE 9. Such means may comprise any
suitable conventional means, such as a conventional relay that is
opened or closed to shut off the power (e.g. from a battery or other
source of electricity) to the pump 54, or otherwise effectively disable
25 the pump 54 by opening or closing valves, or the like; or more
sophisticated components may be provided such as controllers (like
computer controllers), etc. Also the indicator light 79 may light a ~-
different color -- or an additional indicator light 79 may be provided --
_ 2198178
when the full level is being indicated as opposed to three-quarters
level.
FIGURE 10 shows a slightly li~el~t configuration ofthe
components of a vacuum toilet system accoldillg to the present
5 invention. In the embo-liment of FIGURE 10 compoI~ents comparable
to those in the FIGURES 3-9 embo-lim~nt is shown by the same
efel~llce numeral only precerletl by a al".
The all unreinforced plastic combined vacuum and hol~in~ tank
125 is connected to toilet 110 by conduit 111, and includes a vacuum
o differential switch 170 in the top surface thereof, and also a vacuum
relief valve 83, such as shown in cope~ling U. S. Patent application
SN 08/717,904 filed September 23, 1996. An actual dome 84 is
provided in the top surface of tank 125 which contains the inlet pipe
151 for the vacuum pump 153. The vacuum pump 153 may be of very
simple construction, such as an inefflcient air pump (capable of
pumping some liquid if it is flooded), and is mounted on the top surface
of the tank 125. Convention~l check valves 85 may be provided where
desired.
The tank 125 is shown only schematically in FIGURE 10, but is
20 shown -- in one exemplary embodiment -- in more detail in FIGURE
11. As seen in FIGURE 11, the tank 125 exterior surface has
numerous grooves or ~-h~nnels 137, as well as other discontinuities 87,
to insure that no continuous flat surface is greater than about 200
square centimeters. An external fitting 158 may be connected to
25 conduit 116 and have a check valve 85 therein, and extend as
illustrated from the top surface, connected to tube ~.ssemhly 163. The
inlet fitting 138 may also be provided in the top surface of the tank ;-
125. Both fittings 138, 158 may be rotatable in a conventional m~nner
2198178
16
~ for ease of connection to other components of the system of FIGURE
10. In the FIGURE 11 embo~iment a ~ rh~rge pump (like the pump
59) is not provided, but rather the tank 125 would be emptied by
connection to an exterior pump, or the like.
When used for recre~t;on~l vehicles or caravans, the tank
according to the invention may have a ~lilrerellt configuration and size
than as described above, but ~lefelably is generally parallelepiped and
has a contoured, convoluted, discontinuous (e. g interrupted by
grooves, channels, and other discontinuities) exterior surface with no
10 continuous flat area greater than about 200 square cm, and is either
rotational molded or injection molded of all (substantially
unreinforced) plastic.
While the invention has been herein shown and described in an
eminently suitable embodiment, it will be understood that many
5 modifications and additions can be made thereto. For e~mple
equipment for injecting deodorizing chemicals into the tank 25 (either
autom~tic~lly or manually) may be provided, as well as various filters,
stabilizing mounting structures, or the like. Therefore it is intentletl
that the invention be given the broadest interpretation of the
20 appended claims so as to encompass all equivalent structures.
