Replacing the Black Tank Back Flush

[SilverWind]

I have an acquaintance who replaced the plastic anti-siphon valve in his 2016 30' FC because it failed and flooded the kitchen. He replaced it with a brass valve.

[davidceder]

Mine has stopped working a few times. I was able to reach the water line going into mine and disconnect it. Water flowed fine so I knew it was not the check valve or the hose being clogged. I had just enough room to reach up to the hose connection and flush it from the outside and a bunch of gunk washed out but it was still clogged. I took a piece of wire and poked INTO the flush. I guess that unclogged the jets and all was fine until next time which I did the same thing. Has been ok for a couple of years now. I think it happens when traveling with waste in the tank and it just slosh's around a lot.

[Radio Ranch]

I had a similar problem with a black flush that wouldn't accept water. I fixed it with little effort and without removal of the tank.

First, I removed the vacuum breaker and found that there was debris (bark and pebbles) which prevented it from opening. I carefully cleaned it out and reinstalled.

It still would not accept water, so I assumed that the flush head was clogged with similar debris.

Since the pores of the head are smaller that the debris I knew that it would not pass with pressure, so I thought to pull a vacuum on the flush head while having the black tank full of water.

I removed the vacuum breaker, connected the 1/2" line that runs to the flush to a 1/2" female pipe to hose adapter with a hose connected to a shop vacuum. I then filled the black tank to the point where the shop vac was pulling water into the black flush head (in "reverse" direction), and kept the water level in the tank high enough to keep the water flowing into the shop vac.

This technique worked well for me. I now ensure that any hose that is connected to the black flush has a filter on it to prevent debris from entering the black flush valve.

Parts needed: 1/2" FIP to hose adapter (photo attached).

-John

[patrick p]

So many great suggestion. At present the black tank is filled with water containing 2 quarts of Calgon and a cup of liquid dish detergent. Going to let it sit for a few days and see if it has softened the material that is clogging the sprayer nozzels. Thanks again for all the great suggestions.

[aftermath]

Radio Ranch, how did you actually connect the hose you describe to your shop vac? The last photo of the pipe sitting in your toilet keeping the flush valve open is a bit confusing.

As I understand your plan, you cleaned out the vacuum breaker and then connected the pipe from there to the black tank to your shop vac. You vacuumed the water out of the tank and into the vac until it was cleared. Is that right?

[Radio Ranch]

aftermath:

Sorry for the confusion. I attached the wrong photo and couldn't figure out how to change it. I hope that this clarification helps.

I removed the vacuum breaker and cleaned it. I did not reinstall it until the whole cleaning operation was complete.

I soaked the black tank with a full to the brim solution of water and dish detergent overnight (which I dumped in the morning) to attempt to remove any residual solids from the tank.

I connected the FHT203 hose adapter to the pex line that runs from the (removed) vacuum breaker to the black flush head.

One end of the garden hose connected to the hose adapter, then other end was duct taped to the inlet of the shop vac. I used a garden hose that is used to water our garden so as not to reuse a contaminated hose. (No kids here to worry about them drinking from our garden hose).

The flush valve is held open the observe the water level, to hear the suction into the black flush head, and to allow air to enter the black tank as the suction is being pulled. I turned the water pump on and off to keep the water level high enough to provide the flush head with a continuous supply of water.

The effect is to pull a vacuum on the black flush head, such that when the water level in the black tank reaches the head, the vacuum pulls water, which in turn pulls the debris out of the head. I don't think that pulling a vacuum on the flush head alone would do the trick. My guess is that the water is necessary to propel the debris.

It is important to wear rubber gloves and to practice good hygiene when doing this, and to dump the shop vac water where it will do no harm.

From my detailed description, this may sound more complicated that it is. It worked well for me and I learned the lesson of ensuring that I have a filter on the hose that feeds the black flush.

-John

[2000 Excella]

I used your process to unclog my black water tank flush and it worked perfectly! I tried all other methods until I realized that the device within the black tank had to be clogged. Sure enough, debris got in through the hose and was plugged. I purchased the connection that you displayed and bypassed the check valve/bell housing and pulled about 7 gallons from the black tank into the Shopvac which eventually cleared all debris! The black tank flush has never had so much pressure! Thanks for sharing this detail along with photos. I also put a new washer on the exterior connection which now has a screen to keep this from happening again! Thanks again and this works!