Holding Tank Q&A
Where should I put my fittings?
tanks start blank. Your fittings can go wherever you need them for your
application. You can be very specific if you need a fitting distanced
away from any wall or another fitting. The manufacturer will put them as
close as possible to your requirements.
It is recommended to
have all your fittings on the top of the tank. But if you need your vent
and inlet to be on the side of the tank make sure they are as high as
A Diptube for your discharge is the most popular
choice of discharge (at extra cost). A Diptube is a stand pipe that goes
from the top tank, inside of the tank, to the bottom for a more
efficient pick-up of waste (indicated in the photo above). If you need
your Diptube on the upper side of the tank they do provide a 90° pipe
for that application. If you want a Diptube on an odd shaped tank make
sure it is reaching the lowest part of your tank. Otherwise any bottom
fittings for discharge are still an effective and common way to
discharge your tank.
Any fitting on the very bottom of the tank
(for gravity applications) is creating risk of clogging. I would do as
big as a 3-inch fitting and run PVC off of the tank if possible because
it does not permeate (as that line will essentially have constant waste
in it between pump-outs)
What size fittings do I need?
sanitation lines are 1.5-inches. There are only a few applications that
are 1-inch sanitation lines. Make sure you verify what you have
existing or are planning on using when deciding the size fittings you
will need on your tank.
Vent lines are for air displacement
only. Therefore the bigger the better. 5/8" and 3/4" are the most common
size vents for waste tanks and you can go as low 1/2" for water tanks
as the displacement is less rapid.
Do I need separate inlets for two toilets?
do not need two inlets if you have two toilets. You can have the lines join
together before the tank into one inlet. But if you are
worried about clogging or just want to prevent any chances of clogging
due to multiple head use at the same time I would recommend putting two
Do I need separate discharge fittings to go to my Deck Plate and to my Overboard discharge?
do not need two separate fittings to go to the Deck Plate or Overboard
discharge. You can put a fixed Wye or Tee fitting to divert the waste in
the direction of discharge. But if you are more comfortable having one
fitting for each discharge it is a common occurrence to have one for
Do I need an Inspection Port on my tank.
is not necessary to have an inspection port on your tank. If you decide
you would like an inspection port on your tank it is recommended to not
go over a 3-inch port. Anything larger may weaken the integrity of the
tank as the heat from the "Spin Weld" can bow the tanks wall.
How thick are the tanks?
The tanks are a minimum of 3/8-inch thick at it's thinnest place.
Do Polyethylene tanks permeate odors?
does not permeate waste odors. If you have odors in the holding tank
areas please check your hoses for permeation by wiping the lines with a
slightly damp rag and smelling the rag. If you smell waste, the lines
need to be replaced. If you've and any overfilling issues check all of
your fittings and make sure to clean up any waste that may have come out
any paths of least resistance (threaded fittings and vent line)
How are the FPT (female pipe thread) fittings put on the tank?
sticks to Polyethylene. Therefore they take a FPT Poly fitting and do
what's called a "Spin Weld" to the tank. It is a friction weld that
adheres (melts) the fitting to the tank.
Do the tanks have seams?
tanks are Roto-Molded. They do not have any seams. There is a single
hole left on the tank from creating the mold and that hole is patched
with a "Spin-Weld" poly patch.