Why is black water compartment vented?

[SCopp]

Hi all,

We are busy getting our 1973 Overlander in camping condition before the October 2 vintage rally in Gonzales, Texas. My next task will be to get the underbelly put back in place. We added a gray water tank (yeah!) and replaced the old black water pan that was in really bad shape.

Both the old black water compartment and the tank had vents. Can someone explain to me the purpose of the vent for the compartment? I think it vented into the belly pan so it vented into another enclosed space. I cannot figure out its purpose.

Thanks in advance for your advice and counsel.

Susan

[idroba]

Probably the original tank heating system, which had a 2" tube from the furnace to the tank compartments to keep them from freezing (in theory) in cold weather when the furnace needed to run. Often that tube and connection to the furnace has been removed or eliminated, and maybe all that is left is the apparent "venting" of the compartments.