Waste Tank Flush Out Problem

[P&DZ]

Just returned from our first trip with our 2012 Cougar 21RBSWE which we purchased last fall after selling our Rockwood Hard Side A-Frame. The trip went well with no major problems and only one minor (I hope) problem.
After emptying the waste water tank I connected a water hose to the external water connection on the TT labeled “Sewer Water Flush” and turned on the water at the facet. The hose filled with water to the TT connection but did not begin to fill the waste tank. After turning the water on and off several times I started to investigate the problem. I found the flush out water line came through the TT wall under the bathroom sink. Under the sink the incoming water line connected to a black valve with a round body and square head. The water line came out of this valve and dropped through the sink cabinet presumably to the waste water tank. I am not 100% positive but I think the water is not flowing past that black valve. I do not know what this valve is. It is not a shut off valve as far as I can tell since nothing turns or twists. Can anyone provide any insight? What is this valve and is it the problem?

[Logan X]

This valve is the anti siphon valve that stops any black tank water from climbing into a fresh water hose. It is probably installed backwards. You will probably be able to loosen the compression fittings that attach it by hand. There is an arrow marked on it which indicates the direction water will flow.

[JRTJH]

That valve (under the bathroom sink) is called an anti-siphon valve. Its purpose is to prevent "siphoning" of black tank contents through that plumbing system that could contaminate the fresh water supply if siphoning occurred.

One "frequent issue" is that the anti-siphon valve is installed backwards. Remove it, connect the terminal ends to the "other pipe" and it may function. If it does, be very careful, the device is fragile and "slamming high pressure water" on the valve will cause it to leak. ALWAYS TURN ON THE WATER SLOWLY in that system.

If reversing the valve doesn't fix your flow problem, you may have a kink in the PEX line or a blocked/occluded spray head in the tank. I'd first change the valve connections, then look for issues at the black tank PEX line and third, disconnect the tank spray head, reconnect it to a known good supply line and see if the spray head is functional

In any case, changing the valve's orientation usually solves the problem.

[Logan X]

Here is a picture.

[Logan X]

Posting at the same time...

[JRTJH]

Posting at the same time...

Yup.... good thing we're both saying the same thing rather than "opposing views" :lol:

[P&DZ]

Thanks,
I figured it was some sort of anti siphon device. I does have an arrow and the arrow is pointing in the direction of flow, that is toward the black tank. There is no other obstruction or kink in the line to the extent I can see before it disappears under the floor of the cabinet. Do these siphon valves just ever fail ? I don't want to go to the trouble of setting to the spray head someplace under the bathroom floor unless i have to.

[CampNBrew2]

You would most likely access the spray nozzle at the black tank by dropping the underbelly. You shouldn't need to pull up the floor.
It may be as simple as disassembling the anti siphon and cleaning or un-sticking the diaphragm.
The Tornado tank sprayer I installed plugged a few times over the years. Water pressure wouldn't clear it. High pressure compressed air always did. I know, I know, its dangerous:hide:

[P&DZ]

I think I am going to disconnect and repair/replace the anti siphon first, before tackling the tank sprayer, Once I disconnect the anti siphon I should be able to quickly tell if it is the problem or not.

When you say "high pressure" compressed air what psi are you talking about? I go to about 40 to 45psi when winterizing and have not blown anything up yet.

Thanks for you help! I will let you know how this turns out.

[Roscommon48]

Tit is just as easy to fill black water and dump.

Never use the back flush

[CampNBrew2]

I think sometimes it took up to 80psi or so. My sprayer was aftermarket and fed through a section of garden hose with a valve and antisiphon. I kept this tied to my waste line under the trailer for easy access with a quick coupler wyed off of my clear drain fitting sprayer.

Good call on your order of operations. Do the easy stuff first. If the nozzle is clogged, filling the black tank with water to let let the spray head soak may help soften the clog for easier removal with pressure.

[Lee]

Hi,

I have the same TT as you just a year newer which I bought new.

After reading of all of the problems related to this valve,.... Including breakage and flooding the bathroom floor,... I promptly removed the valve replacing it with a brass straight through bought from local HD.

I then purchased a back flow valve that I attach to the end of the hose.

Lee

[P&DZ]

I ordered a new anti siphon valve this morning and will replace it when I pull the camper from storage late next week ahead of our next trip. This time into the Colorado mountains. Hopefully the new valve will fix the problem. If not I will have to determine what my next steps will be. I do like Lee's approach, simple and effective and eliminates the potential flooding issue. Of course it will not fix the immediate problem if the spray heads are clogged.

[pitman44]

Those black plastic things serve two purposes. Vacuum breaker and a check valve. It's not uncommon for them to break. I replaced mine with a brass anti-siphon and a brass check valve.

[srvnt]

Deleted my anti -siphon valve years ago. The only fresh water tied into my flush line is the supply line from outside that I hook up to my flush, which should have a check valve at the source or before it goes into the trailer. So you could possibly contaminate your water source without a check valave , but not the trailers fresh water system, unless you used a contaminated hose/source to fill or use after a flush.

[Javi]

Deleted my anti -siphon valve years ago. The only fresh water tied into my flush line is the supply line from outside that I hook up to my flush, which should have a check valve at the source or before it goes into the trailer. So you could possibly contaminate your water source without a check valave , but not the trailers fresh water system, unless you used a contaminated hose/source to fill or use after a flush.Me too.... and never regretted it...

[jimborokz]

These anti siphon valves are pretty cheap and known to fail often. Most replace them with a quality brass one or just eliminate and use a check valve at the hose connection. I use a separate hose with mine dedicated to that task only. I connect it to a Y at the spigot and use a check valve there so double protection for the water system.