Trying to remember the vent system

[Aktundra]

Doing a shell of restoration of a 1963 Bambi.

Trying to remember how to put things back together.

Looks like I need to understand how the vent system works. Is there usually a line that goes below the floor and is just left open to draw fresh air for the vent system?

[63air]

Any plumbing vents will be through the roof. Your trailer was not built with a grey water tank. If you have the original Thetford waste valve, the grey water came into the valve and dumped on the ground. No vents under the trailer. Rather than try and fit things back , it's probably easier to replumb it and to change the valve.

[TG Twinkie]

You will need a vent stack for the grey and black tanks as well as the galley sink.
The purpose of the vents is to let the air out of the tanks as the liquid flows into the tanks. If there is no vent it will be difficult if not impossible to get liquid to flow into the tanks. It would be even more difficult to empty the tanks.
Depending on the location of the tanks you can use a common vent stack for both tanks.
If you have to make a horizontal run it should slope slightly down hill toward the tank(s). This will allow any moisture collected by the vent stack to run back into the tank(s).

[Aktundra]

Thanks for the comments. A previous comment was correct, I am better off designing my own dump system rather than trying to duplicate the old one.

My question really relates to wether conceptually there should be an "open" end of the vent system under the floor? I think I understand the purpose of a vent, and that it exits through the roof. I am wondering if as a general rule they also usually have an open end under the floor, not directly connected to the toilet or drains, maybe to help with circulation or air flow?

Unfortunately I have not spent much time figuring out the plumbing. At this stage I was really focusing on the frame prep, plywood prep, bending the belly pan, new axel, and my first rivets. Hoped to drop the shell back on the deck, then take my time figuring out, plumbing systems, electrical systems, propane systems, and floor plan etc. Was a last minute realization that I needed to make some water/sewer & layout decisions before even closing up the belly pan.

So my question, there is an "open end" of the vent system above the roof, is there usually and "open end" under the floor as well?

[TG Twinkie]

Nothing below the floor. The vent(s) should exit from the top of the tank(s) and go thru the roof. There should also be a vent behind the galley sink.
You should be able to locate the holes in the shell where the vents were originally routed.
The galley sink does not have a vented bowl like the bath sink, thus the reason for the galley sink vent.

[Minno]

Originally Posted by TG Twinkie

The galley sink does not have a vented bowl like the bath sink, thus the reason for the galley sink vent.

TG,

I disagree with this statement. Not all bathroom sinks have a separate hole in them. The ones we've have in RV's never have. Plus, the extra hole near the top of the sink is an overflow hole, not a vent. I think that's the vent you're talking about about anyway. If not, my apologies.

Regardless, each fixture needs to be vented somehow after the trap. If not vented through the roof, than an air-admittance valve needs to be installed. These are typically installed in the cabinet under the kitchen sink and bathroom sink if there is no through the roof vent for those drain lines. The purpose of the vent or air-admittance valve in the drain line is to ensure good water flow from the sink to the gray tank. The longer the drain run to the tank, the more need for the vent/air-admittance valve.

When we did the venting on Little Girl, we tied the two new gray water tanks and black tank together through a single roof vent. I added an air-admittance valve under the bathroom sink. The tub is on the same drain line as the bathroom sink, so it's covered by the same air-admittance valve. I will add another one under the kitchen sink.

Chris

[TG Twinkie]

Chris: you are correct about the bathroom sink overflow, it is not a vent. Our bathroom sink uses the common vent stack on the 2 holding tanks.
It was early when I typed this.
That's my story and I'm sticking to it. LOL