If your grey (bathroom) holding tank and your (toilet) black holding tank discharge through the same port and each has it's only separate pull handles, you have another option for flushing your black tank. It's called "back flushing." What do you do? How does it work?
First, you need to purchase a Flush King valve that attaches to the drain outlet. A flush king has a clear section in it so you can easily see the contents dumping from your tanks. You can also get a regular valve that attaches to your outlet with no clear section and do the same thing. I prefer the clear section option so I can see what's actually going on.
Like this, click here.
Or like this, click here.
Second, once you attach the valve at the end of your discharge port, completely drain the black tank.
Third, once the black tank is completely drained, close the Flush King Valve and leave the black tank valve open.
Fourth, open the grey water tank valve (make sure the Flush King is closed. This will force the grey water back-wards into the black tank. Don't worry, gravity will not permit any black tank (stuff) to flow into your grey tank. The grey tank has more water in it and will force itself to flow into the black tank. Allow a few seconds for the tanks to equalize.
Fifth, once the two tanks equalize, then close the grey tank valve again. Closing the grey valve at this time will prevent any black tank "stuff" to flow into that tank and it will make it possible to have enough water to repeat these steps again (a second time).
Sixth, drain the black tank again by opening the Flush King. (Grey tank is closes, Black tank is open, Flush King is open).
Let the contents drain until the black tank is complete again. Your first back flush is complete. You can usually repat these steps a total of 3 times if the grey tank is full enough. But, if you can do this only once because you don't have enough water in the grey tank to do it again, that's OK. Once is better than none.
Once, twice, or three times, when complete, there is one final step.
Seventh and final step, close the black tank valve, open the Flush King, and open the Grey tank valve. The remaining water in the grey tank will flush out the sewer hose.
If you do this EVERY time you dump, you'll not need to use the black tank flusher sprayer at all. It saves water, and it keeps your black tank cleaner.
If you have a washing machine in your camper and it's plumbed into the grey tank for the bathroom, the washing machine soapy water back flushes into the black tank..... cleaning it out .... real nice! No extra water needed.
