Need this identified please

[FishCampers]

Can anyone tell us what these two white water lines are for? At least, we assume they are water lines. They are found under one of the sinks in the bathroom vanity. Thank you.

[prndl]

Air Gap installed in the black tank flush line.

[Mikendebbie]

Based on my reading the forum - those are notorious for failing and flooding your RV. Many folks replace them with brass vacuum breaker (similar to the pic below) or cut the thing out and simply tie the lines together permanently. I have not yet replaced my two vacuum breakers (I have two black tanks) but it is on the list.

[DutchmenSport]

That is the check-valve for your black tank flusher. You attach a garden hose to your black tank flusher in your convenience center and turn shore water spigot on. Water flow through a separate water line (the white line). It will travel through that pipe under your sink. That black "thing" is a check valve, which allows water to flow only one direction. This way, there is never any back-feed from the black tank that could feed backwards from the black tank BACK into the garden hose or worse, back into the campground (or your hosue) water system.

It is important to have that check valve in place, but sometimes when they fail, folks will remove them completely (not a good idea though). Others will be a little beefier model, like the one pictured above in the prior post.

But, that is what the white pipes and and black "thing" connected to them is.

The only time you'll have water in that line is when you flush your black tank via the black tank flush hook-up in your convenience center. And yes ... when you winterize, you do need to either run some RV pink stuff antifreeze through that line, or at best, blow it out. It does hold water and it will freeze up and break if not winterized, just like the rest of your water lines.

Happy camping!

[High5er]

I think many of these fail because people aren't using pressure regulators when they flush their black tank. I've seen a number of people (and I've done it too) just hook the hose up and let 'er rip. I thought mine was failing because it started leaking then realized I was putting unregulated pressure through it. Remember, these are the same quality as other plumbing components in your trailer.

[BB_TX]

This is the black tank flush system.

[Foldbak]

OK.... now I'm embarrassed I've been here a while and read a lot about this. I didn't know it's location or the potential fubar it could cause. I thought it would back flow at the convenience center. Going to upgrade, I back flush a lot! And this could also cause black tank odor?

[BB_TX]

Be glad yours is under the sink. Mine was in the wall between the shower and the entry closet. And it started leaking. Bad. Had to cut an opening in the back of that closet to get access to remove that antisiphon/vacuum breaker valve. Connected the pipes together and added an external vacuum breaker valve.

[Mikendebbie]

Below is rough schematic for where my vacuum breakers are located. If you don't know where your vacuum breakers are located - look for them so you know where they are just in case. The one I colored red will flood the basement if it goes bad. The one I colored green will flood our front bathroom and bedroom if it goes bad.

[Ahdmeyer]

i have looked but never found them. anyone know where they may be in a 2020 3931 fb? would like to replace with brass if i could find them.

[Mikendebbie]

Jdarwin (2019 3931FB) shows photos of the vacuum breaker located behind the basement wall near the back of the wet bay in post #18 in this thread from April 2022. In post #19 I show the location of the 2nd vacuum breaker. Look for an access hatch in the lower closet.

https://www.montanaowners.com/forums...ad.php?t=86736

[FishCampers]

Thank you everyone! You've been very helpful!

We know all about back flushing the black tank as we've owner motorhomes for 13 years, but just hadn't run across anything like what I posted in my opening post.