Originally Posted by never monday
BUT...replace the hose (5/8") between the pup and the bowl with a longer section and a vented loop up high.
While I agree this is the usual and recommended installation
and the following may be regarded as a bit adventurous by some, the following is an alternative for the Jabsco (or similar) which in many boats will result in less pipework and ease of hiding the anti-siphon loop. Some may like to try it, but whatever, as Pat says, if the toilet is below the waterline fit a loop one way or another.
If one uses an anti-siphon loop similar to the Forespar ones one can put it on the suction side of the toilet's pump by doing the following. Take the top cap off and remove the little duck bill one way valve. Replace it with a small block of soft porous foam (a small piece cut off window or door draft
strip is ok) large enough so that is is squished up a bit when you screw the top cap back on.
The foam has enough resistance to air flow so that it does not leak enough air to affect the pump suction but is porous enough so that it lets down the water
level in the loop when you stop pumping. It also does not leak (at least no worse than the dribble one sometimes gets from the original duckbill valve) as when there is water
in the loop the loop is under suction from the pump.
Doing this means that between the head's pump assembly and the bowl you just have the short piece of plastic hose the toilet comes assembled with. To/from the pump is just the suction for the flushing
water and the black water discharge from the pump. The anti siphon loop can be hidden away in a locker.
By doing this one avoids the untidy second set of hoses to get to the loop and back and makes it easier to hide the loop away.
When this was recommended to me by our boatbuilder
I did a
but agreed to it and it has worked perfectly - has been like this for many years. I had also thought it would forever need cleaning to remove salt
buildup but again that has not proven to be so - I squish the bit of foam out in fresh water around once every blue moon.
If doing this I would recommend checking that it is working as planned by when pumping stopped put a bit of water over the top of the valve and see if it gets sucked in as the water drops in the anti-siphon loop. Obviously, as always, the loop should also be above the highest waterline.