Black Tank Flush Anti-Siphon valve replacement
Having read thru a couple of the threads on the Black Tank Flush anti-siphon/vacuum-break valve I came to the conclusion mine was fouled up.
I dreaded trying to locate it between the walls but it turned out to be easy. In my 2008 22' Sport, it's found by looking inside the wardrobe. On the aft wall of the wardrobe was an 8" X 8" wood panel held by two screws (what's that..?? an access panel..??) and removing the two screws revealed the anti-siphon valve attached to the PEX plumbing via two simple, 1/2" threaded screw-knobs, similar to what is often found beneath bathroom sinks and toilets which use flexible hoses at the shut-off valves.
One of the other posters expressed considerable frustration in attempting to dispense with the anti-siphon valve and using brass angle fittings instead. He had trouble with leaks. I suspect that was due to the fact the screw knobs do not seal against the /2" pipe threads when fitted up against the a-s valve..but use the rubber gaskets/O-rings inside the fitting and ordinary 1/2" plumbing fixtures do not provide for that. Teflon tape and thread sealants also will not work.
I found a simple solution to replacing the a-s valve. (Yes... I know... the a-s valve is a plumbing code thing... but it's really overkill when you think about it. The system is not continuously hooked up to public water so a back-siphon is not going to occur unnoticed.) My valve was filled with what looked like tobacco leaves.... an insect nest apparently. I cleaned it out successfully but upon examining the valve I discovered the vertical plunger/seal can spit a little water out in between the walls of the Airstream and I don't care for that a lot more than I worry about a little siphon action on a system that is never allowed to remain hooked up without pressure applied to itl
Anyway, here's the SIMPLE SOLUTION I used: go to Lowes or Home Depot. Obtain two "Shark Bite" or "Blue Hawk" 90-degree-angle slip fittings for PEX pipe. They cost about $5 ea. Using an ordinary PVC cutter, cut the existing PEX just below the two hand-knobs which screw to the valve. Be certain to cut the PEX to the same height. If you cut the risers about 3" shorter you can use one piece in the next step.
Using a short piece of PEX, connect two slip-fit 90-degree angles to each other, then to the PEX risers. (Connect the two slip fittings to each other with a short 3" piece of PEX you just removed.)
FINISHED! The flush line is fully connected and will work perfectly.
In other words, the supply side of the flush line rises up to a 90-degree slip fitting, which is connected to another 90-degree slip fitting which sits atop the PEX going to the black tank flush sprayer. The two slip fittings are well above the black tank which should prevent any sewage from ever making it over the "hill" to escape the system, especially if not left connected before or after the flush-operation.