Looking for help

[ready2retire&drive]

I would like to install two better vent caps on my black tank covers on the roof. I contacted Jayco to ask which two out of the four are for the black tanks they could not tell me. I'm sure someone has changed theirs. I have the 37rb 2015 Seneca model. So four vents up top is a fifty/fifty shot as to which are which. I appreciate any advice and help to make sure I don't mess up , thanks gord

[Lake Huron]

My Northpoint has 5 tanks, 3 grey and 2 black. I have 3 vents on the top of my trailer. My front grey tank drains a little slow and the front black drains just fine. Since there is only one vent in the roof toward the front I was thinking it was a missing vent issue. Since my tanks were empty, I fired up my leaf blower and had the wife open up the dump valves and blow air backward thru the sewer line into the tank, she is afraid of heights and was not going on the roof. I was on the roof by the vent and could feel air blowing out of it. I had her close the grey tank and open the black tank and do the same thing. I felt air coming out the same vent, and it was a little more smelly so I knew it was the black tank.
I would try the leaf blower trick, as long as your tank is fairly empty, and see which one it is up there.

[ready2retire&drive]

Thanks will give that a try appreciate the quick response, gord