Gray Water/Grey Water is normally your soapy water plumbing and holding tank.  Sink Water and Shower Water.

Our objective is to design and install a sink, shower, and toilet system that requires no vent stack sticking up through the roof. Sticking with our wants of keeping our Sprinter as stealth looking as possible.

A toilet is on the Black Water system.  See SPRINTER BLACK WATER SYSTEM

This leads us to our Gray side of things.

Trying to eliminate the roof vent presents some problems to solve that typical plumbing systems incorporate.  We are hoping our idea will function as we think it will.

One of the issues to eliminate, are any water filled P-Ttraps, that are traditionally used to prevent holding tank gasses from stinking up the living compartment.  These don’t work that great anyway.  RVs that sit any length of time often have all the water evaporate naturally.  Then tank smells can permeate the interior living space.   Many RVers wonder why their rig have a stink if left sitting without use.

We are eliminating the typical water filled P-Trap by using  HEPVO Drain Traps.

Also once a holding tank is added under the van some type of venting is required to serve a couple of purposes.  While we have eliminated the under floor black holding tank, we still need a gray water holding tank.

Again a common vent pipe through the roof is normally used to vent any stink up and out of the roof.  Secondly and just as important,  the vent serves to equalize the holding tank  pressure build up as water fills the holding tank.  Also to prevent negative pressure when draining the holding tank.

Logic says you can’t simply leave a hole in the top of a holding tank to vent pressure.  Any water that reached the top of the tank due to travel and sloshing around would simply spill out.  The high vent going out of the roof typically solves this too.

In our case we are going to use an air venting valve mounted on the top of the holding tank.  A type that will pass air.  But plug when water attempts to pass upwards through the valve.  The valve will close momentarily when water attempts to pass.  If this all works as planned we will eliminate the roof vent pipe.