Back Flushing the Black Tank

I’d buy one of the clear add on flush adapters with gate valve and back flush my tank that way... you can also back flush the grey tanks... I’ve been using one of these adapters in three different RVs for many years...

You can see what’s com8ng out of those tanks, the gate valve keeps you from getting unpleasant mess when opening dump cap ,

I’ve never used the built in back flush on current fifth wheel and don’t intend to.. I don’t want a flooded bathroom due to an unexpected anti siphon valve fail

vent pipe

Mine had a kink in the hose between the aerator under the sink and the black tank. same symptoms you experience.fixed kink and works...make sure the 2 fittings at the aerator are tight also.

Old-Biscuit wrote:
Look inside bathroom sink cabinet.....
Black Tank Flush System has a anti-siphon vacuum breaker device

It is either installed backwards or the nozzle installed in the sidewall of black tank is plugged

OK I see what you are talking about and will remove it later today and check it out to see if it is stuck they couldn't have installed it backwards because it has worked correctly for 5 years.

eHoefler wrote:
Do you have the drain valve open to the tank?

I have tried it both ways.

Do you have the drain valve open to the tank?

I had the same thing happen on just one occasion; hooked up a hose to the black tank flush at a CW and it just wanted to blow back at me. So i just skipped flushing that time.
I don't know what caused it but it never happened again.

Look inside bathroom sink cabinet.....
Black Tank Flush System has a anti-siphon vacuum breaker device

It is either installed backwards or the nozzle installed in the sidewall of black tank is plugged

Lack of venting. Check your tank vent.