Originally Posted by CraigCam
I have decided to add a grey tank to my 1970 Overlander. I will have the kitchen sink dran to fitting and then the shower and bath sink into another one. I really want to limit the number holes in the sub-floor. My question is, I know I need to ventilate the tank, can I vent it through the the tub and sink drain pipe or does the vent need its own fitting into the tank?
Hope this makes since.
The purpose of a vent through the roof in a trailer is:
1. to let air into the tank when the tank drains,
2. to let sewer gas out as the tank is filled,
3. to keep a vacuum from being created within the pipes that sucks liquids out of the traps.
One vent will suffice, as long as it does all of these things.
However, proper placement of air admittance valves (Google Studor Vent) can make it easier to do with one vent.
Some people say to not combine the black and gray vent, but one vent through the roof will function properly if all of the above conditions are met. Black water and gray water piping should not be connected except at the vent, and that connection should be high in the trailer (at a minimum higher than the sink rim), so that no cross contamination of waste water can occur.
The kitchen sink, lavatory sink, and shower waste water piping are all connected to the gray tank. The new vent from the gray tank runs combined with these three fixtures, or use air admittance valves. One gray water vent has to penetrate the roof separately or connect to the existing black tank vent at a level above the sink rim.
The black tank and existing vent function as they exist, except to connect the gray tank vent, if you choose to use the existing vent.
Of course there are many options. You have to choose what you want.