Black Tank leakage, possible BT flush sprayer


Problem: Anyone have any idea where the BT spray head and is installed and how to inspect it? Read below for more details.

I have a 2011 RW 305 that I purchased about 3 months ago. We are FT it right now. I have noticed a sewer smell around the furnace venting for about a week, so I cracked open Youtube and started my research. This is my journey to identifying the actual problem:

1) Flushed all tanks extensively (2 grey and 1 black) and added the eco concoction to all.
2) setup sewer dump hose with a U to prevent sewer gas from backflowing into RV
3) removed the front storage area access wall to visually inspect the connections. the smell was very strong and I was getting close.
4) validate the roof vent pipes and back washed them to verify they were clear and properly venting.
5) removed the toilet, GI cleaned and verified all seals were working properly.
6) dropped the front section of underbelly and 20 gallons of waste water quickly greeted me.

problem found, now I looking for the root cause.

I cut the front underbelly section on the cross brace support beam and removed it. That is definitely installed first and not easily removable. The gas line was mounted directly over the belly cover screws. PITA!! Once removed I tested the system. I have noticed that when I use the BW tank flush, water drips down both sides of the tank. So, I most likely have a leak around the flush sprayer on my black tank but I have yet to verify this because I can't find where the flash sprayer is installed. Anyone have any idea where the BT spray head and is installed and how to inspect it?

Or if you think it could be another issue, please post.



Well-known member
Before going to the sprayer, check the anti-siphon valve for leaks. It's usually located behind the shower controls. If you have a 6 inch round access panel in the shower, or an access panel behind the shower wall, open it to check the valve.

Here's how it looks on a Bighorn, from the other side.



Staff member
I would look for a braided white (kinda opaque) hose and follow that to the black tank. With luck that hose just came off of the sprayer fitting.



Well-known member
Also check all of your gray water drains, sinks and shower. We had the shower connection work loose and started to leak. After tightening it all is now good. When it came loose, it moved just enough to allow water to miss the drainpipe. This could also allow the smells you are experiencing.


Prolifically Gabby Member
I agree with Dan. If you've got water cascading down both sides of the tank when you use the flusher, the Anti-Siphon Valve is the likely culprit since it's mounted higher than the tank and known to fail. If it were the connection to the actual tank flusher, methinks you would only get water down the side of the tank it's inserted into.

If you can easily access it, replace it with a real brass one. The cheaply molded plastic OEM one is garbage.


Well-known member
I agree that the black tank flusher anti-siphon valve is a very common failure point. The only thing that bothers me about blaming the flusher valve or flusher system is that flushing is done with pressurized FRESH water into the black tank. The 20 gallons of WASTEWATER you found above the corrugated underbelly don't agree with the FRESH water used for flushing leaking.

I am thinking you have a crack in a tank or other wastewater plumbing. Sorry!!!


Well-known member
I think the flush valve is on the end side of the black tank. If the hose connection is compromised, it'll leak when using and leak out when the tank level reaches the valve port.


Prolifically Gabby Member
I think the flush valve is on the end side of the black tank. If the hose connection is compromised, it'll leak when using and leak out when the tank level reaches the valve port.

The sprayer is on the end of the tank. The ASV is a different animal and is mounted higher than the tank in the line between the sprayer and the inlet for the flushing system.
It’s supposed to be a vacuum breaker to prevent backflow from the tank if overfilled. In reality, it’s a flood waiting to happen.
20 gallons (or what looks like it) would be possible if it’s been leaking for some time and not finding it’s way out of the sagging underbelly or into the actual living space. In my case, it was running out under the stairs to the bedroom and onto the kitchen floor.

Simple way to identify the leak for sure is to crawl up in the rear of the basement while someone turns on the water to the flusher momentarily.

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Prolifically Gabby Member
And the tank flush sprayer is usually mounted on the end opposite to the outlet valve. And Bobby A., your PM to me was closed so I replied to your email address.


OK, I have identified the problem. It is the black tank flush nozzle seal to the black tank. Once I pulled the underbelly, it was easy to identify when the flush system was turned on. The dripping around the tank bottom was occurring once the tank level was higher than the flush nozzle.

Has anyone every replaced one of these? What did you replace it with? The nozzle just installed on the side of the tank with no mounting flange. The tank is not flat in this area so a flat plate will not easily mount.