Black tank venting

[772ark]

Black tank question:

If the black tank is mounted under the bus do you have to run a air vent up through the floor of the bus and out through the roof, or can you just go up out of the tank then turn it down towards the ground and keep it all on the outside?

[Twigg]

If you vent it that way, it will smell.

That's why they are usually vented high and out of the way.

[Jameson]

I was going to try a vent output towards the bottom with a homemade carbon filter to collect odors. I've used the method to collect fermentation odors in small scale ethanol production, and it worked flawlessly. You would need to replace or clean the carbon once it was saturated.

Worth a try if you want to avoid another hole in the roof.

[JDOnTheGo]

To avoid smells, the tank should have two vent lines. This allows air to circulate. Ideally, one of the vents is up high (roof) and has one of the roof vent/covers that draw a slight vacuum (like this) when the wind is blowing.

I've never had a coach with the tank vented near the ground but can imagine you will smell it (think dumping the smell at ground level right next to where you are sitting in your lawn chair).

[JDOnTheGo]

Duplicate post - apologies...

[Iceni John]

Like JD, I believe in having two vents per tank to promote a good airflow through the tank - this helps the aerobic bacteria do their thing (they're the ones that help break down the tank's contents and prevent smells). My black and gray tanks are next to each other, but separated by a frame rail between them. Each tank has two 2" vents, in diagonally opposite corners of the top. The black tank's left rear vent connects to a vertical pipe that exits through a forward-facing louver in one of the covered-over side windows, the black's right front vent connects to the adjacent gray's left front vent via a short U-bend under the frame rail, and the gray's right rear vent goes down to road level just ahead of the differential and exits through a venturi aimed backwards. When driving, air is blown into the black's upper vent, down and into the black tank, out the black and into the gray, and sucked out of the gray at road level. When parked, the flow reverses, with fresh air entering the gray at ground level and eventually exiting the black at its louver vent which is just under the roof level. This all sounds more complicated than it actually is - I just want a flow of fresh air through both tanks, and a way to vent away any methane that accumulates.

John