1/2 bath black tank flush system

[Pirates55]

Anyone with a fifth wheel that has a 1/2 bath in it have a factory installed black tank flush on the 1/2 bath. The folks at palomino or Sabre tell me they can add one at the factory due to RVIA building codes requiring a "pop valve" being required. This pop valve has to be higher than the highest water point in the unit. This makes no sense to me. Why would a pop valve for the black tank in the back have anything to do with the plumbing up front. The tanks aren't plumbed together. Can someone explain this to me.

I'm curious if this is the case for all fifth wheels with a bath and a 1/2.

At first they send me an email that says it will be added to the unit but not 100% sure where the hook up would be. Then they send me one the next day saying this about the RVIA Building codes. I'm not sure what will be on the unit when it arrives.

[ependydad]

Sounds like it won't be there. I'm not sure why the 2 tanks have anything to do with each other, but I do know that the "pop valve" on the main black tank is typically in the wall behind the shower or sink and corresponds to the "highest point" comment.

I had a RV Service center add one after the fact. It was $30 for the part and $125 or something like that for labor (because I wanted it installed above the under layer insulation). In hindsight, it would have been a pretty easy install.

[Pirates55]

What is the pop valve?

[ependydad]

Honestly, I had never heard that term before. But, I'm assuming it is a backflow preventer to keep waste water from flowing back through the black tank flush.

[BigJohnD]

It's a backflow preventer, or anti siphon valve. We always cut them out and use an inline one (at the inlet or on the hose) and a designated hose. I've had too many of them have a sticking valve, and dump water wherever they're mounted. Unfortunately sometimes inside the wall. On our new fifth wheel, the main bath one is / was under the master bath vanity. First test and it dumped water under there with the sticking valve. A few pex mods later and it's gone. By code they have to install them, or suppose to, and they have to be above the level of the toilet. If you have one, just check it every now and then, as they can leak. It was a problem on our Mobile Scout, Tiffin, and now this one.

[Pirates55]

Are they mounted in the wall or just under the sink. Are they easily seen and checked??

[BigJohnD]

All depends on the make / brand. I have never not been able to get to them. Some were just harder to get to than others. On one, I had to remove the living room TV and remove a panel to get to it in the wall. I reconfigured the plumbing and just did away with it. While flushing the tank, I think it's just a good idea to go check it and make sure it isn't leaking, if you can see it. There's nothing wrong with doing away with them, provided you use a designated hose. Some of the black flush kits you can buy come with an inline anti-siphon valve that go between the hose and flush line, some don't come with one at all. You can get the inline type at lowes or HD usually.