Gray water drainage design help (see drawing)

TakingThe5th wrote:
Maybe I'm missing something, but is there a way you could somehow tie the drain lines together below the floor while keeping the valves above the floor? With the drain lines coupled you could at least equalize the level in the tanks when necessary and also be able to dump tanks with one hose. If you dump the kitchen first, then the shower, your hose will also be cleaner for stowing.

The shower tank needs to be lower than the shower drain, which is more or less at floor level, ergo the shower tank needs to be below floor level. If there's room enough for a larger tank, there could be a single combined tank below floor level, which would simplify things somewhat and gain some useful cabinet space.

This latest revision actually looks nearly workable to me, at least in the basic overall plan. The connection between the tanks via the vent line is the biggest problem; it should be a separate connection with a valve. With the connections as shown, if water is flowing from the top tank to the bottom tank, the air being displaced from the bottom tank has no ready exit. Also, with no valve, once the bottom tank fills up you can't use the kitchen sink even though the top tank is empty or the shower drain will overflow.

There also needs to be a trap for the shower drain, either one built into the drain itself or a separate P trap underneath. Without it, odors from the tank will enter the RV. (Shower water will get nasty after sitting for a week or so, just like dish water will.)