Join Date: Jun 2016
Location: Orange County, CA
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
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.