Venting black tank?

[Mtrdrms]

Hello fellow bus builders!
So I'm working on the plumbing and I'm wondering about venting. How have you done it? I have a one way vent under my sink and I have a 3" pipe going into the tank (I'm not a plumber) so

1) do i have to put an additional hole in my tank for a vent?
2) what size and where do I vent it?

I have my tanks under my bus and I dont want to run a vent pipe through the roof like a camper would so I'm a little stuck. Any thoughts?

Thanks

[Iceni John]

Black and grey tanks must be vented to allow methane to escape, and to provide fresh air for the aerobic bacteria to do their thing. This means using a decent-size pipe that exits upwards (methane is lighter than air). Every setup I've seen has only one vent pipe, and that doesn't make sense to get a natural flow of air through the tank. In order that my grey and black tanks are thoroughly vented while moving and when parked, I've come up with a slightly different solution. My two waste tanks are next to each other but separated by a frame rail, and each tank has two 2" vent fittings rotomolded into their top surfaces. Both tanks' front vents are interconnected together, the grey tank's rear vent goes down to just ahead of the differential and points backwards, and the poo tank's rear vent goes up and exits out of a blanked-off window behind my driver-side closet with a louver grill that faces forward. When driving, air is forced into the louver grill, then through both tanks and is sucked out of the grey tank by venturi effect, and any smells are left behind at road level. When parked, the flow naturally reverses with cold air entering at ground level and flowing though both tanks, then exiting out the high vent after it has warmed slightly in the tanks. This way I have plenty of fresh air for the bacteria, and absolutely zero smells when driving or when parked. It sounds more complicated than it is, but it works very well.

John

[SAge59]

John,

Do you have a rough diagram of your set up? It sounds very interesting and might consider it for my build.

Thanks

[Iceni John]

Originally Posted by SAge59

John,

Do you have a rough diagram of your set up? It sounds very interesting and might consider it for my build.

Thanks

No, sorry. All my engineering drawings and blueprints are in my head! It was more work to vent my tanks this way, but I think it's well worth it.

John

[Danjo]

Here’s a website that have a good article on an RV sanitary plumbing system

Above and Below: Understanding the RV Waste System | Trailer Life

[kazetsukai]

Originally Posted by Mtrdrms

I have my tanks under my bus and I dont want to run a vent pipe through the roof like a camper would so I'm a little stuck. Any thoughts?

I have two grey tanks joined with a Tee that I vent underneath the body (instead of a roof vent). How I did mine below.



I got 1 1/2" Tank grommets:
https://www.amazon.com/gp/product/B01MD1JDK8


Drilled the hole in the top of each tank, and then installed the grommet and an air admittance valve from Home Depot:

[PNW_Steve]

Venting the grey tank that way may not be a problem, the black tank is another story.

In warm weather the black tank can vent some nasty smells. I prefer to have the black vent as far away from me and as high as I can.

[SAge59]

John,

so both tanks have 2 vents. One forward and one aft.
when you drive air is naturally pushed into the tanks to aerate them.
For the back vents, how do you ensure that it does not overflow or spill out when you drive?

Thanks

[kazetsukai]

Originally Posted by PNW_Steve

Venting the grey tank that way may not be a problem, the black tank is another story.

The grey tank can get quite funky too. The right thing to do is probably go up to the roof for both, drilling another hole through the floor then ceiling. Ugh...


I think I have to do this anyway for the composting toilet. I wonder if I could tee into a vent all the way to the roof.

[PNW_Steve]

Originally Posted by kazetsukai

The grey tank can get quite funky too. The right thing to do is probably go up to the roof for both, drilling another hole through the floor then ceiling. Ugh...


I think I have to do this anyway for the composting toilet. I wonder if I could tee into a vent all the way to the roof.

Yes it can. Not as bad as the black though

I lived for two years in my trailer with a composting toilet and, unlike the black tank, I would vent it out the side of the bus.

If you are running a composting toilet you don't need a black tank.

For the OP: I have seen rigs with the vent pipes coming, individualy, through the floor and up about a foot and 90 into a "T" and then a single vent from the T up through the roof. It's probably obvious but to be safe don't tie your fresh water tank into a shared vent.

You can run the fresh water tank vent in the manner shown in the picture.