Black Tank Flush

Question

So..... yesterday I was flushing out my black tank in preparation for a weekend outing to our local lake. As I always do, I hooked the water hose up to the hose connection specifically for that purpose, and I began to let the water flow....of course, with the black tank dump valve open and the sewer hose running into the sewer receptacle. As the process went on for a few minutes, I noticed that there was water dripping on the ground from beneath the water heater area. On closer inspection, it was leaking from a red pipe under the bathroom vanity where it connected to what appeared to be a vent. There is one red pipe coming up to a brass fitting with a silver top and another red pipe exiting that brass fitting going back down. Again, I assume it is an internal vent for the black tank flush, because as soon as I turned off the water, the leaking stopped. It looks to be a fairly easy fix to correct the leak, except for the cramped space trying to work inside the bathroom vanity.

Am I correct in saying that the black tank flush has its own vent? And would it be under the vanity like that? Or is this connected to something else that I need to be concerned with? Any ideas or help would be most appreciated!!

downtheroad · Answer

The "vent" you are referring to is probably the anti-syphon (anti back flow preventer) device. They can sometimes emit water if the incoming pressure from the hose is high.

In a previous trailer, mine would "leak" from time to time. I just laid a towel under it to catch the water when I was flushing the tank. It didn't fix it but did solve the problem.

You can replace the valve, but like you said it's in a difficult working space.

bb_tx · Answer

Agree it is the antisiphon/vacuum breaker valve. And they do sometimes put them under the vanity. Just be glad it is not inside a wall as is mine. Mine was a plastic valve that cracked and flooded the floor.

If it were me, I would replace it rather than contend with a continuing leak.

anti siphon/vacuum breaker valve

Google it and you will find different manufacturers and prices.

dutchmensport · Answer

My Outback did more than 'drip' a little. Last Spring, I completely flooded the front half of the camper inside for this very reason. I finally figured it out it was the anti-syphon on the hose for the black tank flusher. It's located under my bathroom sink, very accessible. I've not replaced it yet so simply am not use it. Actually, I think my simple wand on the end of a garden hose stuck down the toilet works much better. But this is on my list of things to fix this spring. Should be an easy fix to replace it.

Looking back, I think the reason it broke to begin with, was because I failed to winterize it properly. I blew that line out with my air compressor, but I really don't think it completely cleared all the water out of the anti-syphen valve. When freezing weather hit, it broke the valve.

FYI.... mine is plastic, not metal. If metal, I don't think would have broken.

10forty2 · Answer

As always, you folks are awesome! That's exactly what it is (anti-siphon valve) and where it's leaking is not the valve itself but the plastic coupler that goes into it. It may have frozen and cracked....not sure I got that place winterized properly this winter. I'll use extra caution for now when flushing out my tank, but I'll get that fixed after this trip. Now, to figure out how to contort myself so I can fit into that little bitty space.... I guess yoga is in order..... ;-)

Thanks!!

1brynelson · Answer

Personally I'd find a small teenager with mechanical skills to crawl under there. I went and looked at mine. It's far enough back that I'd have to get at least 1 of my shoulders inside the cabinet and there's no way that's going to happen and still be able to see what I'm doing. I'm to wide at the shoulders. That's a problem I run into all time trying to work on this rig.

Forum Discussion

Black Tank Flush - Leak Inside

About Motorhome Group

Related Content

Black Tank Flush

Black Tank Flush

Black Tank Flush Vacuum Breaker

black tank flush hook up