380FL Rear Black tank vapor lock?

[Brian Rhoda]

I had a previous trailer with a similar issue. It ended up being a clearance problem between the vent pipe and the cap on the roof. The pipe was left too long and when the cap was placed on it there was only a narrow gap between them. This created an insufficient air flow. I cut about an inch off the the pipe and reinstalled the cap. It improved the flow.

Truckster,

I did check one vent cap earlier, but may have checked the wrong tank. Will have to use a sniff test to check it out this time!

[Jkwilson]

Keith,

Appreciate the input, BUT. Bought the rig new 12/20/22, had it for less than a week when I noticed the issue. No way on earth we got a poop pyramid that quick (there's only two of us). That is also a 50 gallon tank and I always have 5 - 10 gallons of water in it before we use it. That helps disperse the incoming loads & discourage any baby pyramids. Also do a 30 - 40 gallon flush every time I dump tanks. Takes time, but I am NOT getting a pyramid!

The camera will help diagnose regardless of the reason. Mine has an 11’ probe, so I could go in the vent and down to the tank if needed.

I know it may seem silly spending money figuring out a warranty problem, but you don’t want a dealer bumbling around trying to find it.

If the tank burps when empty, have you tried flushing with the dump valve open? If you have an appropriate place to do it, I’d unhook the sewer hose after flushing the tank, and try flushing the toilet with the valve open. Accomplishes two things: It will vent an empty tank, so if the vent is your issue, it should go away when the valve is open and then return when you close the valve. It will also 100% confirm the tank is draining.

[Jlawles2]

You may be able to use a tape measure to measure all the way to the bottom and also to the bottom of the vent tube by hooking the end of it.

[Brian Rhoda]

Figured this thing out about 10 days ago, since my little tweak the venting has been fine. Up on the roof there are 4 separate vents - 1 for each tank (2 gray, 2 black). The vent caps are a 2 piece deal. One is a flange mounted to the roof that sorta holds the vent from the tank. No cement, it's just confined inside the ring. There is a separate cap that sits on 8 little fingers and is secured with a screw. I took off the cap on the offending tank and peered down into the abyss. Had a real good LED lamp and with that I could actually see the surface of the tank contents. This verified that the vent was clear. When I put the cap back on, I didn't sock it down tight, just made sure it wasn't going to fly off on our next travel day. Went back inside and did a few test flushes - no burps! Been flushing fine ever since - no matter the "load" involved.

Thanks for all the ideas. In the end, it was the simplest approach that worked - this time.

[Jlawles2]

You might be able to cut a couple of VEE cuts on the back side so that if / when the cap gets snapped down, it has a way to vent.