Black tank flush leaking/broken

[audio1der]

Yesterday while emptying our tanks, the black drained nicely. I kept the slice valve open and turned on the black tank flush to get the worst of it out before filling/emptying a few times as usual. But no water came out of the black tank, and there was water going into the black tank flush inlet. Then I saw & heard it' water gushing out of the underbelly right over the curb side suspension.
Do I have a burst line? I don't think its the vacuum valve, as there was no water inside the trailer or under the bath sink.
Thoughts?

[JRTJH]

Was the water coming out of the underbelly clean or black tank contents?

If clean, you may have dislodged the hose connection from the anti-siphon valve to the tank rinse fitting or possibly it's been broken all along and finally failed ????

You also say that you rinsed the tank for a while then filled the tank a couple of times and nothing came out. It is possible that the handle on the dump valve separated from the blade and although the handle is moving, the tank valve remains closed (nothing coming out the sewer hose). If you kept filling the tank while you were trying to find out why nothing was coming out, you could have overfilled your black tank, so if the water leaking from the underbelly is black tank water, you may have split or ruptured the tank by overfilling? I know, not a pleasant thought, and hopefully not the reason for your leak, but something to consider if the water is "dirty water" that's leaking.

[audio1der]

It was only clean water leaking. It began when we turned on the flush, and stopped when we stopped the "tap" water. The knife valve still works 100%, as tested by filling the black tank via the toilet instead of the flush inlet.

I need to get under there and remove some belly enclosure :(

[JRTJH]

If it's clean water, check the 1/2" PEX where it is clamped to the tank spray fitting. They sometimes aren't tightened well at the factory and a bit of "extra" water pressure will cause the hose to pop off the sprayer. Remember, there's no "backflow valve" that close to the tank, so don't use your black tank and fill it over about 1/3 full or it may leak through the spray head and drip into your underbelly.

[chuckster57]

I've seen a few of those clamps fail. It takes a special tool to put them on and I have gotten lucky a few times re crimping. You can buy the tool at hardware stores, but they aren't cheap (I bought my own), I would venture its cheaper to pay an hour of labor at the dealer.

[JRTJH]

If you don't have a PEX crimping tool, many hardware stores will "rent" you one for about $5 if you buy the PEX clamps from them. It's a "fool proof" tool in that once you start crimping, you can't get the tool off the clamp until it's properly tightened. The "failure" comes from not positioning the PEX tubing all the way onto the fitting or in placing the clamp too far back on the hose.

If you "feel you must buy" your own tool, they are available for about $20 on EBay, not the "snapon" quality, but as good as (or better than) Harbor Freight. I bought mine from EBay about 10 years ago when they were $4.99 with free shipping. As much as I use it, it's still working, so must have been an "OK" tool LOL

[rjsurfer]

My leak on the flush system was right at the connection point of the tank. The screw fitting was just hand tight when I opened up the Coroplast.

A few turns and all was well.

Ron W.

[audio1der]

After talking with the parts guys and service guys, I walked out with a new vaccum (?) valve for under our sink, just up from where the black tank flush line enters the trailer. Turns out there wa swater inside the sink storage compartment. I didn't have any silicone to seal the plastic to plastic connection so I have to go back and then let it cure before testing, hope this fixes it. All connections were screw-on plastic fittings but in good shape, no lines appeared to be split.

JRTJH- you mention there is no backflow valve that close to the black tank?/ I was going to buy a backflow preventor last season but was assured every RV had one there. I now think I need a black tank flush pressure regulator AND a backflow preventor piggybacked when I use the black tank flush?

[gepaine]

The manufacturer of my black tank flush kit recommends that you DO NOT use any kind of pressure regulator on it. I assume that is because you need full pressure to get the best flushing.

[JRTJH]

After talking with the parts guys and service guys, I walked out with a new vaccum (?) valve for under our sink, just up from where the black tank flush line enters the trailer. Turns out there wa swater inside the sink storage compartment. I didn't have any silicone to seal the plastic to plastic connection so I have to go back and then let it cure before testing, hope this fixes it. All connections were screw-on plastic fittings but in good shape, no lines appeared to be split.

JRTJH- you mention there is no backflow valve that close to the black tank?/ I was going to buy a backflow preventor last season but was assured every RV had one there. I now think I need a black tank flush pressure regulator AND a backflow preventor piggybacked when I use the black tank flush?

What I intended to convey with this statement is that there is no "backflow valve" mounted on the outside of the spray fitting that's mounted in the black tank (on the factory installed device) so if you disconnect the tubing at the tank, the spray head that's mounted in the tank will now be "open" and can leak black tank contents back into your RV underbelly.

There are some CAMCO (and another brand) aftermarket black tank rinse systems (that come with a clear hose) that do have the anti-siphon valve mounted directly to the tank spray device. But that's not how factory "OEM" systems are installed.

As for not using a pressure regulator on the tank rinse system, there's "mixed opinion" on that. The rinse system, like most RV water systems are rated at about 60 PSI. If you connect it to a 20 PSI water supply (or regulate down to that) you will get "ineffective" rinsing because of low pressure. On the other hand, if you connect it to a 130 PSI water supply, you may "blow the top off your anti-siphon valve" !!! So, use some "common sense" in what pressure you connect to your black tank rinse system!!! Mopping the underside of the sink vanity cabinet is not fun even though it's only "clear water" :(