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Old 09-01-2019, 07:39 PM   #1
Skoolie
 
Join Date: Dec 2018
Location: Colebrook CT
Posts: 163
Year: 1989
Coachwork: MCI
Chassis: 96A3
Engine: 6V92
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?

Thanks
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Old 09-01-2019, 11:46 PM   #2
Bus Nut
 
Join Date: Jun 2016
Location: Orange County, CA
Posts: 919
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.

John
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Old 09-29-2019, 09:58 AM   #3
Mini-Skoolie
 
Join Date: Jul 2019
Location: St Louis
Posts: 13
John,

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

Thanks
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Old 09-29-2019, 11:28 AM   #4
Bus Nut
 
Join Date: Jun 2016
Location: Orange County, CA
Posts: 919
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
Quote:
Originally Posted by SAge59 View Post
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
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Old 09-29-2019, 12:23 PM   #5
Bus Crazy
 
Join Date: Sep 2018
Posts: 1,375
Year: 2007
Coachwork: Thomas Built
Chassis: Minotour
Engine: Chevy Express 3500 6.6l
Hereís a website that have a good article on an RV sanitary plumbing system

Above and Below: Understanding the RV Waste System | Trailer Life
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Old 09-29-2019, 04:17 PM   #6
Bus Nut
 
Join Date: May 2017
Location: Windham NH
Posts: 693
Year: 1999
Coachwork: Amtran
Chassis: International RE
Engine: International T444e
Rated Cap: 76
Quote:
Originally Posted by Mtrdrms View Post
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.
ima_2d5869d.jpg


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:
ima_800a2bc.jpg
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Old 09-29-2019, 07:22 PM   #7
Bus Geek
 
Join Date: May 2016
Location: Eastern WA
Posts: 6,337
Year: 2002
Coachwork: Bluebird
Chassis: All American RE (A3RE)
Engine: Cummins ISC (8.3)
Rated Cap: 72
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.
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Old 09-30-2019, 09:19 AM   #8
Mini-Skoolie
 
Join Date: Jul 2019
Location: St Louis
Posts: 13
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
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Old 09-30-2019, 09:55 AM   #9
Bus Nut
 
Join Date: May 2017
Location: Windham NH
Posts: 693
Year: 1999
Coachwork: Amtran
Chassis: International RE
Engine: International T444e
Rated Cap: 76
Quote:
Originally Posted by PNW_Steve View Post
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.
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Old 09-30-2019, 11:48 AM   #10
Bus Geek
 
Join Date: May 2016
Location: Eastern WA
Posts: 6,337
Year: 2002
Coachwork: Bluebird
Chassis: All American RE (A3RE)
Engine: Cummins ISC (8.3)
Rated Cap: 72
Quote:
Originally Posted by kazetsukai View Post
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.
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