The "P" or "S" trap (plumbing)

[hampstead38]

We have two 30-gallon gray tanks slung under the Overlander, each with a standard unthreaded opening for a black ABS pipe. On the galley side, it's easy enough to plumb the kitchen sink down to the tank with a normal ABS "S" trap. On the head side, I'd prefer to avoid raising the shower floor any more than necessary (to allow room). Even squeezing in a shallow "P" trap will force me to raise the floor.

These are only gray water tanks so the issue is slightly different than in a household. On the other hand, having some kind of water (or mechanical") seal does afford certain advantages. Any thoughts, master plumbers?

[Over59]

I ran a 1/2 hose and a serie of reducers from the shower drain back up thru the floor to a small jetflo pump. Pumps the shower into the gray tank, which I then use to flush my marine head. I set it up so I can drain it with a garden hose connector also or on to the ground. Not enough head room to raise the floor.

[ticki2]

Grey water can have very nasty odor , you still need some form of trap. Fernco makes rubber traps that may work for you , or even a rubber hose with a low enough bend to stay filled with water.

[hampstead38]

I can run a shallow "p" trap, but it will require cutting some floor or building an elevated shower drain pan.

[Jammer]

Me, I'd cut the floor to make room for the trap. You can then box it, and insulate it, if you want.