Black water tank flush

I've never heard of this happening. Thanks for the heads up.

When I try to flush my black tank, nothing happens. Hook up the hose and turn on the pressure and the hose gets full but no flushing. Is it possible that the check valve froze closed and is now stuck? I suppose the best thing to do is start taking it apart to see what's going on.

Had this happen on my trailer's black flush anti siphon valve. Took valve apart..found 2 dead stink bugs that wedge themselves in a fashion that kept valve from closing. After removing this bug debris, reinstalled valve and has worked flawlessly since. I think dealer wanted around $40 for new valve.

eocamper wrote:

BB_TX wrote:
You are not doing anything wrong. Those anti siphon/back flow preventer valves are common failure items. Time to replace it.

Removing the valve is an option. But you need to use an external back flow prevention valve if you do to prevent the unlikely, but possible, backflow of water into the fresh water source.

Thanks for the reply. I thought this hose goes only to the black water tank. How is it possible to get into the fresh water source? Figured it was a connection to a hose with a check valve as a safety feature in the event you forget to open the black water drain valve that goes directly to the black tank.

The black flush is separate from the fresh water in the trailer but not the fresh water of the campground, that is what is being protected.

Old-Biscuit wrote:
DO you use a water pressure regulator for city water hose AND black tank flush hose????


Yes...backflow preventer under sink leak. Some because they get cracked from freezing temps, some from high pressure being used (they have an air gap) that is how they break vacuum.

It really didn't don on me to use a pressure regulator to flush. Looks like I'll replace the check valve and go from there.

DO you use a water pressure regulator for city water hose AND black tank flush hose????


Yes...backflow preventer under sink leak. Some because they get cracked from freezing temps, some from high pressure being used (they have an air gap) that is how they break vacuum.

Codes require many water systems, lawn sprinklers for example, to have back flow preventers. When water pressure in the main water line is lost, water flowing out of the pipes at low points causes a suction in the higher levels that can siphon water back from any water line connected to it. Now that would not suck water from your black tank flush unless you were flushing at the same time water pressure were lost. Not likely, but certainly possible.

Check valves are because some fausets don't have back flow preventers

BB_TX wrote:
You are not doing anything wrong. Those anti siphon/back flow preventer valves are common failure items. Time to replace it.

Removing the valve is an option. But you need to use an external back flow prevention valve if you do to prevent the unlikely, but possible, backflow of water into the fresh water source.

Thanks for the reply. I thought this hose goes only to the black water tank. How is it possible to get into the fresh water source? Figured it was a connection to a hose with a check valve as a safety feature in the event you forget to open the black water drain valve that goes directly to the black tank.

It is normal for these valves to expel water. Just get rid of the stupid thing and make sure that the check valve works. RV manufacturers don't care where they place these valves or follow the instructions.

valve instructions