Holding Tank Plumbing

[Lee Hadjiosif]

I'm planning on replacing my 20 ga holding tank with a Ronco Poly. Currently my aluminum tank has a pumpout fitting on the side at the highest point which I assume must have a dip tube attached to an elbow. There's no room for a top fitting. My question is: should I go for a high side pumpout with a dip tube again or a low side. No room for a loop at the bottom so it has to be straight out. I understand that the bottom discharge will empty more stuff out, but is there a problem with having the discharge hose always full of "stuff" and the possibility of leaking versus top discharge. Thanks.
s/v Calaloo

 

[Ed Schenck]

Peggy would definitely say no to a bottom discharge. I had Ronco do a top discharge on mine. If you do not have space then they will do a side discharge. But you really do want what you call a "dip tube".

 

[Chuckbear]

Lee, I know Peggy will have something to add to this, but we are kind of in your same situation and our only option is a bottom discharge. I considered long and hard about stuff sitting in the discharge hose. I installed a 1 1/2 inch valve 6 inches from the connection to the tank. It is easily accessible for me and it is closed in normal use and opened only for pump out and flushing. It is not ideal, but boats are compromises. Chuck

 

[alexco38]

The first few feet with ABS

If you must use bottom discharge, just put the first few feet (below the top level of the tank) with the black ABS stuff. Use a short (6 inches) Trident hose to connect the tank to the ABS tube. ABS doesn't peameate. Dip tube never can get to the bottom of the tank.

I believe most pre-made tanks are bottom discharge.

 

[Peggie Hall HeadMistress]

Don't put words in my mouth...

I would NOT say no to a discharge fitting at the bottom of the tank. Although ideally, it's best to put ALL the fittings on the top of the tank, that requires at least 5" clearance about the top of the tank...which makes it impossible on many tanks, leaving no choice but to put the discharge at the bottom and the inlet and vents at the tops of vertical surfaces.

Alex has the right idea: use hard pipe--ABS or plain ol' PVC as far as the top of the tank, then switch to hose. Dometic/SeaLand has the fittings needs to do this.

However Alex is wrong about dip tubes...they can actually get closer to the bottom of the tank than a fitting on the side or end of it can. Measure to actually touch the bottom of the tank with the tube...then cut it at about 25 degree angle. It's only when the tube is cut straight across the bottom that it has to be any higher than 3/4" off the bottom. The opening in a spinwelded fitting on the side or end of a tank is at least 1" off the bottom.