Black tank flush

[JDZO6C5]

We replaced our Rockwood TT this past March and took our new 5th wheel cougar lite out for the second time. Brought it back today and went to dump the tanks. As I was dumping the black tank I started using the black tank flush, which is where the issued occurred. The flush on this cougar isn't very strong it seems compared to my last camper. I would shut the valve on my old camper to let the flush build up some water in the tank and release it. I would do this a few times to make sure I got everything I could flushed out. So of course I performed the same method on our new cougar. I started the black tank flush, which was getting into the tank and slowly coming out into the dump hose. Then I shut the black tank valve closed to let some water build up in the tank with the flush; one minute later I see water leaking just off to the right of my entrance stairs under the camper. I shut off the water and went into the camper and saw water going across the hall from the bathroom leaking below the floor when going against the wall. The water was coming from under the bathroom sink. I'm assuming the design on the keystones cougar is different than our prior Rockwood and have to have the tank valve open while using the flush at all times. My question is if there is something I need to repair under the sink in the bathroom where the water leaking out? It doesn't seem like I need to and appears to be a relief valve of some sort under the sink?

[bobbecky]

It sounds like the air gap/back flow preventor for the flush system is located under the sink. It must be broken, which is where the water is coming from or possibly a hose connection was not properly made.

[Desert185]

And its probably a good idea to use a water pressure regulator. The plastic BT flush system can be fragile. I have two. One for the potable supply, white hose and one for the green BT flush hose.

https://www.amazon.com/dp/B003BZD08U/ref=asc_df_B003BZD08U5068267/?tag=hyprod-20&creative=394997&creativeASIN=B003BZD08U&linkCode=df0&hvadid=167146990738&hvpos=1o4&hvnetw=g&hvrand=5113335754918019694&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9030882&hvtargid=pla-274070646123

[canesfan]

x2 on both the above ^^^ . Sounds like it's the vacuum breaker or whatever you want to call it. They are very well known for leaking. It's probably either shot or maybe just a loose connection. The usual culprit is forgetting to winterize the BT flush port. A lot of users replace them with an elbow and add their own backflow preventer on the hose. They tend to stick them up under the sink or behind the shower wall. And a pressure regulator is always a good idea on the BT flush also.

[JRTJH]

Here is a picture of the FRAGILE plastic anti-siphon valve that's located under your sink. It's way up high, probably behind the sink and very near the fittings that connect the faucet to the hot/cold water supply tubes.

That anti-siphon valve is, in my opinion, the weakest link in the trailer's entire plumbing system. It's made of plastic, doesn't survive freezing, won't stand up to high pressure use, won't make it through the winter unless removed and dried (or RV antifreeze is used to flush all water from the device).

I think you'll find the source of your water isn't the "black tank flush" but rather the "black tank anti-siphon valve".

Many have simply removed it, used two right angle fittings and a 1/2" plastic nipple to create a "bypass". Most of them also added an anti-siphon valve outside their trailer at the black tank flush fitting. Others have adapted a more "robust" brass anti-siphon valve to replace the cheap plastic one. Whatever you do will be an improvement over the current "almost $50" plastic junk.

I've also added a "block diagram" of the black tank flush system to more fully depict how the system is laid out in your trailer.

[NealBlue]

If the black tank is vented through the roof then what is the point of the valve? I can't understand why the flush water can't be allowed to just spray into the tank. Is it supposed to prevent the water, or whatever else, from coming backwards through the flush plumbing?

[Desert185]

If the black tank is vented through the roof then what is the point of the valve? I can't understand why the flush water can't be allowed to just spray into the tank. Is it supposed to prevent the water, or whatever else, from coming backwards through the flush plumbing?

Prevents reverse flow that would contaminate the fresh water source/supply. Confidence inspiring with such a cheap back flow preventer...

[JDZO6C5]

Thank you everyone for the great detail in your replies! Much appreciated! JRTJH, thank you for the pictures as it makes sense to me now as to what happened. My 5th wheel is brand new, so I wonder if dealer would replace with a brass valve, but then I think it would be easy for me to do it instead of my 5th wheel sitting at the dealer for at least a month due to the busy season.

[JDZO6C5]

And its probably a good idea to use a water pressure regulator. The plastic BT flush system can be fragile. I have two. One for the potable supply, white hose and one for the green BT flush hose.

https://www.amazon.com/dp/B003BZD08U/ref=asc_df_B003BZD08U5068267/?tag=hyprod-20&creative=394997&creativeASIN=B003BZD08U&linkCode=df0&hvadid=167146990738&hvpos=1o4&hvnetw=g&hvrand=5113335754918019694&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9030882&hvtargid=pla-274070646123


I have always used a regulator for the potable water but never for the black. Lesson learned and will get a second one now! Thank you Sir!

[JDZO6C5]

Also what does the bottom here mean in caps?

[chuckster57]

The fitting you attach your city water too has a one way valve in the center. If you take the screen/washer out it looks like a button in the center.

If there is pressure in the water system, it will spray back at you and can put the valve " off center" so it won't seal. It's important that it seals when not hooked up to city water and running the water pump.

[canesfan]

Also what does the bottom here mean in caps?

To expand on what chuckster said above, the little cheap plastic city water check valve is very delicate and can be very easily broken (kind of like the black tank vacuum breaker). I had one break all by itself in the middle of the night with the pump on and it proceeded to pump 80 gallons of water from the tank into the basement. I suggest not messing with it unless it IS broken.

Edit - I guess I should add that I have a small hand pump I pump antifreeze into the city water inlet so it gets winterized, too. They are suggesting that you just push the valve in to drain the water left in that part of the system, usually not much at all. That may, or may not, work sufficiently to keep the valve from freezing.

[eds451]

Well, all this talk about the vacuum breaker/check valve in the black tank flush system caused mine to get jealous and quit. Mine was located right behind the hose bib on the wall. No service, no wake, just an unceremonious burial in the trash bin.

[slow]

The flush on this cougar isn't very strong it seems compared to my last camper.


Many of us have found the ptex line for the black tank flush kinked and requiring a repair with the installation of an elbow. In our case, the kinked line was below the water inlet and visible by removing the comoplast.



Sent from my iPhone using Tapatalk

[JDZO6C5]

So today was the first time I got back into the 5th wheel to check out this vacuum flusher check valve under the bathroom sink where the water was coming from. I didn't get the time to troubleshoot it when the leak occurred. I just stopped the water, wiped up the water on floor and left it at that. So I was checking out this check valve and it turns out it was loose! One full turn and it was completely detached from the water line. Based on this, I'm guessing that it may not be broken, so I just tightened it up and hoping next time around it won't leak again, but I will definitely have my eye on it and get an extra set of hands to turn on or shut the water off when I use the flush next.

[JDZO6C5]

Another question, this was right next to this valve and it appears loose as well should this stay the way it is or should it be tightened?

[chuckster57]

That's the vent for the sink. It's okay if it's loose, as long as it's threaded enough not to leak gases.

[JRTJH]

You probably found your leak, tighten the anti-siphon valve fittings and always ALWAYS use a pressure regulator with the black tank flush system. That fragile plastic fitting will "self destruct" if you "slam it with full pressure" from a city water supply source, so use a regulator and always turn on the water slowly so you don't "hammer" the internals....

The other picture you posted is a "cheater vent" that allows your sink to drain without gurgling. If it's not securely screwed into the drain line you can hand tighten it but don't overtighten it. There is no water in that part of the drain lines. The only purpose for that vent is to allow air into the system so the water will drain without the gurgles.

[CrazyCain]

I read some where that if you never use your toilet facilities, you'll never have any problems and can sell the rig like "new".. :lol::D:popcorn::popcorn::popcorn:

[ctbruce]

I read some where that if you never use your toilet facilities, you'll never have any problems and can sell the rig like "new".. [emoji38]:D:popcorn::popcorn::popcorn:
Trailer for sale. Never smoked in. Never pooped in. Almost like new! $27,000 new. Asking $30,000 for pristine condition. Serious inquiries only.

Sent from my SAMSUNG-SM-N910A using Tapatalk

[CrazyCain]

Trailer for sale. Never smoked in. Never pooped in. Almost like new! $27,000 new. Asking $30,000 for pristine condition. Serious inquiries only.

Sent from my SAMSUNG-SM-N910A using Tapatalk



:lol::lol::lol::lol:
:popcorn::popcorn:

[Jackstraw]

I had the issue. I had my wife turn the water on while I watched under the sink. It was the connection of the plastic tube to the outlet attached on the outside. Specifically, the female connector is too long and it runs out of threads on the male connector of the outlet. Therefore it doesn't seat the washer and no matter what, it was loose. I went to the hardware store and bought a flexible hose of the same length with the proper female connectors (one was metal one was plastic) with built in washers. snugged right up $4.79 solution.