[John]

Jon,

I have two roof vents … One for the fresh water tank and one for the black tank. They don’t mix. I believe the grey is vented thru the four individual plumbing fixtures under the two sinks, shower, and washer.

I don’t make stuff up unless it relates to D.C., and then anything you say these days people will believe!

[Gerald]

OK, as long as they are separated that is good. But how can a vent to atmosphere build up air in a tank? As water is drawn it is replaced by air and as water is added it displaces air. That is why a tank has some provision for admitting and exhausting air,

But none of that explains why a 120V pump introduces air into the plumbing system unless the tank is virtually empty, surely not 1/2 full. BTW, I don’t have any issues with the concept of switching to a low current draw 12V pump when not on a 120V power source but the stated reasons sure sound silly.

[Larry & Diane]

It still makes no sense. Maybe it is just a Marathon build quirk since it does not appear to bother anyone else. But I still call BS on the buiding pressure in the tank. Can’t happen in any normal way.