Black tank flush valve

[33 RLDS]

What I hate about mine is the inlet connection is directly above the fresh water gravity fill inlet. When you unscrew it, water drips down on the inlet vent and cap. Granted there should be a one way valve installed but it still bothers me.

[Atlee]

Fortunately on my 23RB, the black tank flush inlet is on the rear of the trailer. And the fresh water gravity fill, and city water inlet are on the side.

Originally Posted by 33 RLDS

What I hate about mine is the inlet connection is directly above the fresh water gravity fill inlet. When you unscrew it, water drips down on the inlet vent and cap. Granted there should be a one way valve installed but it still bothers me.

[vcbice]

First, I am one of those who bypassed the anti-siphon valve. The rest of this is why they are there in the first place so you can make an informed decision about removing one.

The valves are there for a reason. The outside hose connection is below the level of the toilet. So, if you overfill the black tank, sewage could flow out that connection. So, the pipe has to run higher than the toilet valve.

Then, with the hose connection lower, it could create a siphon condition where the hose fills with sewage and then out. The siphon action would pull sewage out of the tank and that could contaminate the fresh water line that you are connected to. The anti-siphon valve is added above the level of the toilet for that reason.

The anti-siphon valve is required by code so the mfg puts them in.

What I wish they would design is an anti-siphon valve with a 'drain/vent' line that runs outside the unit. This would prevent the valve from flooding the trailer if it fails.

[Bassdogs]

Well decided to proceed on this fix today. After looking carefully I was able to make put together a bypass with 2 male fittings on a 2 " pex tube. That worked great but after hooking the whole thing up, I still had a drip drip leak where the thru the wall input was connected to the pex. Put a new connector on the pex but it still leaked when I got it all back together and remounted the input fixture outside. So the original mod is done but I am waiting a couple days to receive a replacement input mount. The new one has a brass male connector compared to the plastic oem mount. Hoping that fixes the thing.

Thanks for the explaination on why the valve is there in the first place. My outside connection is high on the side of the TT so not a problem with a syphon. My oem valve is in the trash and a new one will NOT be installed.

Did I mention I hate plumbing?? Now I have to go out to the TT and wipe off all the blood stains on the shower stall, sink cabinet door, and a couple other places from the scratches on my forearms. These 70 year old arms tear with just a touch on anything rough. My arms look like I got in a fight with a cat. I will get a chance to heal a bit while I wait on the replacement parts.

[Atlee]

Fortunately, on the 23RB, the outside hose connection is well above the toilet.

Originally Posted by vcbice

The valves are there for a reason. The outside hose connection is below the level of the toilet. So, if you overfill the black tank, sewage could flow out that connection. So, the pipe has to run higher than the toilet valve.

Then, with the hose connection lower, it could create a siphon condition where the hose fills with sewage and then out. The siphon action would pull sewage out of the tank and that could contaminate the fresh water line that you are connected to. The anti-siphon valve is added above the level of the toilet for that reason.

[BigJohnD]

Most are up high, or above the tank. Matter a fact I've never seen a black flush inlet (oem) at tank level except one on our class c we had. Most of the aftermarket set ups are mounted at tank level. Every manf I know of mounts the back flow valve at or above toilet level.

[Atlee]

Would a back flow valve be needed if the water inlet was higher than the toilet?

Originally Posted by BigJohnD

Most are up high, or above the tank. Matter a fact I've never seen a black flush inlet (oem) at tank level except one on our class c we had. Most of the aftermarket set ups are mounted at tank level. Every manf I know of mounts the back flow valve at or above toilet level.

[BigJohnD]

To me, if the water inlet itself is higher than the tank, I see no need for the valve, but that's just my opinion.

[Bassdogs]

Happy to report that I successfully completed this project. Flush valve is gone and a new brass inlet mount is installed. I had 2 issues. Ist was the back valve and second was a cheap oem inlet mount. Any time you had spray outside where the hose connected it leaked into the fitting. The second one was what caused the drip drip drip I reported a few days ago.

I can now put this mod/repair on the completed stack and move on to whatever is next.

[DC8Captain]

Originally Posted by Bassdogs

Happy to report that I successfully completed this project. Flush valve is gone and a new brass inlet mount is installed. I had 2 issues. Ist was the back valve and second was a cheap oem inlet mount. Any time you had spray outside where the hose connected it leaked into the fitting. The second one was what caused the drip drip drip I reported a few days ago.

I can now put this mod/repair on the completed stack and move on to whatever is next.

Hey Bassdogs - Can you post a picture of your completed mod please.

Thanks,
Dale

[RVhiker]

Originally Posted by Atlee

Would a back flow valve be needed if the water inlet was higher than the toilet?

I think you would need at least a vacuum breaker.

In system without a vacuum breaker, if the hose is still connected to the black tank flush and is disconnected from the faucet supplying water, then the end of the hose would be lower than the black tank and could siphon out black tank liquid onto the ground. Under different circumstances, black tank liquid could be siphoned into the water supply system.

[vcbice]

What he said.

It is a code thing.

[RVhiker]

Originally Posted by vcbice

What he said.

It is a code thing.

For sure, I don't want to siphon out black tank water onto the ground - or into the general water supply; both of which could spread disease to other people.

We all know how easily siphoning can happen - reference the many posts about siphoning water out of the fresh tank via the overflow lines.

[Bassdogs]

If you tip your TT too high changing a tire on the other side, you might have a problem. Come on guys when you're done flushing the tank, you turn off the water and disconnect the hose at the water inlet on the TT. Not real hard to keep a syphon from happening. It may be a code thing, but I'm now out of code compliance I guess. Let the code people come to my aid when the valve they require causes my TT to flood. If they want compliance then have them require a fool proof valve.

I don't want to confess to too many code violations so I will stop on this one. With the valve out of the system and an inlet above the toilet level, there will not be a problem unless you fall asleep during the process.

[vcbice]

Don't get me wrong, I got rid of the valve in mine as well so my trailer is not in compliance either. I was just stating why the valve is there in the first place.

[DC8Captain]

To those that have had valves fail what exactly failed? Did the valve assembly housing fail (crack in housing) causing the leak or did the plunger and inside parts fail causing your leak?

[Bassdogs]

Originally Posted by fdhealy4

To those that have had valves fail what exactly failed? Did the valve assembly housing fail (crack in housing) causing the leak or did the plunger and inside parts fail causing your leak?

In my case the internals in the valve got messed up and water sprayed in under the sink thru the vent. Not sure how that happened but it is supposed to lock the vent and allow the water into the tank. Instead it only partially blocked the vent allowing a ton of water to flood the inside of the TT.

[FeatherFam]

Nice job, Bassdogs! 70 years young makes you an DIY inspiration! I will be doing this soon, too.