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Old 09-01-2019, 07:39 PM   #1
Almost There
Join Date: Dec 2018
Location: Colebrook CT
Posts: 88
Year: 2000
Coachwork: Bluebird
Chassis: A3RE
Engine: Cummins 8.3
Venting black tank?

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?

Mtrdrms is offline   Reply With Quote
Old 09-01-2019, 11:46 PM   #2
Bus Nut
Join Date: Jun 2016
Location: Orange County, CA
Posts: 847
Year: 1990
Coachwork: integral
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
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.

Iceni John is offline   Reply With Quote

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