Black Tank Vacuum Breaker

dougrainer wrote:
1. The OUTPUT of that check valve is the Black connection. Loosen it and start the Black Flush. IF water seeps out the check valve is NOT your problem. It is the tank nozzle is clogged.
2. I have NEVER seen or had a check valve get clogged by debris. Possible but in the hundreds I have fixed never a clog. They either are connected in reverse which means they will not work, or they LEAK due to the seals have failed. 99 times out of a hundred, the Tank nozzle is clogged with debris. The ONLY fix is to pull that nozzle and clean it out or replace if cleaning is not want you want to do.
3. The ONLY way the Tank nozzle can get clogged is because you allow the Black tank to stay above 3/4 full for too long and the dirty water migrates thru those small holes and when you dump, that dirty water dries out and the solids dry out and clog those holes. Doug

It's starting to sound like it almost has to be clogged nozzles. We have to camp without water and sewer very often, so we often end up with a full black tank that doesn't get dumped until we get on the road. We _always_ use the black tank flush when we have access to water -- that is until the current it-won't-work status. And the people we bought the RV from have the same schedule as us so probably .... well.... let's just say it may have been inevitable.

So, now ... I guess I get to go looking for this nozzle.

Do you have any ideas? Will I need to remove the black tank?

Thanks for all the help.

MY "RInse" tube ?
uses an external hose attachment in the WET BAY

i think i like that system better

older_fossil wrote:
A couple of comments. I spend a lot of time on the Tiffin Owners Forum and the black tank flush comes up often. The usual cause of the flush not working is the flush jets in the tank get clogged with debris and minerals. A lot of folks remove the sprayer and drill the holes out slightly larger (3/32"). Also, many folks have had those plastic vacuum breakers fail and start leaking inside the coach. Tiffin has changed to a brass vacuum breaker and check valve on newer coaches, and Tiffin parts can sell you the brass replacements. Or you can buy them cheaper at places like Amazon.

Tiffin owners forum. Now there is a valuable resource:R Drill the holes out slightly larger???????? Well, lets see, larger holes will cause LACK of a forceable jet spray in the tank. It will also cause MORE dirty water to easily get inside the nozzle. The PROBLEM is that people let the tank level stay above 3/4 and the dirty water migrates inside the nozzle. Then lack of using the Flush when dumping allows that dirty water to stay inside the nozzle and dry out and clog. Doug

PS, NOT debris and "minerals". HUMAN WASTE, which I guess you could call Minerals and debris:B

While doing the GEO tank flush, I turn off the water pump and I have a small block of wood to hold the flush valve open. Costs: zero, and it works quite well.

A couple of comments. I spend a lot of time on the Tiffin Owners Forum and the black tank flush comes up often. The usual cause of the flush not working is the flush jets in the tank get clogged with debris and minerals. A lot of folks remove the sprayer and drill the holes out slightly larger (3/32"). Also, many folks have had those plastic vacuum breakers fail and start leaking inside the coach. Tiffin has changed to a brass vacuum breaker and check valve on newer coaches, and Tiffin parts can sell you the brass replacements. Or you can buy them cheaper at places like Amazon.

1. The OUTPUT of that check valve is the Black connection. Loosen it and start the Black Flush. IF water seeps out the check valve is NOT your problem. It is the tank nozzle is clogged.
2. I have NEVER seen or had a check valve get clogged by debris. Possible but in the hundreds I have fixed never a clog. They either are connected in reverse which means they will not work, or they LEAK due to the seals have failed. 99 times out of a hundred, the Tank nozzle is clogged with debris. The ONLY fix is to pull that nozzle and clean it out or replace if cleaning is not want you want to do.
3. The ONLY way the Tank nozzle can get clogged is because you allow the Black tank to stay above 3/4 full for too long and the dirty water migrates thru those small holes and when you dump, that dirty water dries out and the solids dry out and clog those holes. Doug

Old-Biscuit wrote:
Well that IS a black tank 'anti-siphon vacuum breaker backflow device' installed on the water supply line for the black tank flush system

With hose connected to flush system water comes in up thru bottom hose and LIFTS that disc up which then seals off that top cap which is open to atmosphere and then pushes spring-loaded check valve open so water flows out and down the hose on left side

Being CLEAR you can see what does/doesn't move when water supply is turned on.

BUT usually when they fail water blows out top cap and leaks inside RV

IF water doesn't flow it is usually due to the nozzle being clogged.

Thanks for the good description -- gives me things to check when I get where I can hook up to water, probably this weekend. Thanks again.

GPWayne wrote:
From the picture, I would say the black wire tie is putting the Vac-breaker in a bind. It does not take much to jam plastic valves (Over a period of time). I would replace the tie on just one line and see if you can tie the other in a way not to put the valve in a bind.

Now to fix the valve. (With water OFF) Remove the valve, the fittings should be very close to finger tight. If not, that could be part of the problem. When you get it out. Carefully open the check valves (should be easy to tell what is stuck). Lube with plumber's grease ONLY. If it frees up and seems that it should be OK.(If not replace) Reinstall, FINGER TIGHT and leak check.

If you still can't get flush water into the black tank. It's time to attack the check valve where you attach the hose to flush system. That is where I would have started. This check valve normally fails OPEN but you never know. (Make sure you don't have a plugged screen washer, failed pressure regulator or something like that) I also hope your not using your drinking water hose for all this.

Let us know what you find, please.

Thank you. I'm not parked where I have access to water right now (but should be this weekend).

But ... If I shake it, it rattles, which I took to be a good sign that it might be working, and that it might not be the problem.

darsben1 wrote:
That is a fresh water Vacuum breaker. If it went bad no fresh water would go in the bowl
BY Flush your black tank what do you mean.
Toilet won't flush
Cannot empty black tank
Your Black water tank flush system does not work.

Sorry for the confusion, I mean my black tank flush system seems blocked - no water goes into the black tank from the black tank water input.

Well that IS a black tank 'anti-siphon vacuum breaker backflow device' installed on the water supply line for the black tank flush system

With hose connected to flush system water comes in up thru bottom hose and LIFTS that disc up which then seals off that top cap which is open to atmosphere and then pushes spring-loaded check valve open so water flows out and down the hose on left side

Being CLEAR you can see what does/doesn't move when water supply is turned on.

BUT usually when they fail water blows out top cap and leaks inside RV

IF water doesn't flow it is usually due to the nozzle being clogged.