[DutchmenSport]

Don't know how your drain pipes are configured. I've got 3 valves. One is for the kitchen sink in front of the tires. The other two valves are tied together in a single outlet behind the tires.

All my campers in the past have always had the black and grey tank valves run together to one outlet. I learned early a simply, quick, and water saving method to keeping the black tank flushed out, very, very well.

I purchased a Flush King valve that bayonet mounts to the drain outlet. The Flush King type valve has a clear section so you can always see what's coming out. Attach the Flush King type valve and do the following.

Close the grey tank valve and drain the black tank completely until it stops or almost stops running. The water is gone. BUT... there is still stuff on the bottom of the black tank ... after you've done this a few times you'll never NOT do it again.

Once the black tank finishes, close the Flush King valve and now open the grey water valve. The grey tank is full of water, the black tank is not. Water runs down hill. As soon as you open the grey valve, the grey water will back-flush into the black tank. This takes only about 5 to 10 seconds and then close off the grey tank again.

The grey water back flushing into the black tank will help break away any residue left on the bottom of the black tank with the backward “swish”.

Now, open the Flush King valve again and let the black tank drain again. Once it finishes draining, repeat the back flush. If your grey tank is full, you can comfortably back flush 3 times. Each time, more and more, and more “stuff” will come gushing out of the black tank. And you’ll never go back to a simply flush once and go again when you see how MUCH is still in the tank with only the initial draining.

After the 3rd back flush, close off the black tank valve and finish draining the grey tank to clean out the sewer hose.

After you’ve done this a couple times, you’ll find it goes pretty fast. Once you see how much comes out the second and third time, you’ll be taking longer showers so you’ll have more water in your grey tank so you can back flush a 4th or even a 5th time. And YES, I have found by trial and error that back flushing pulls a lot more out of the tank than my black tank flusher. With that clear section in the Flush King, you can easily see what’s coming out.

If you have the luxury of time, follow up with your black tank flusher. As a final, add water to the tank, add a half cup of Dawn Dishwashing liquid down the toilet and head to your next destination. Your sensors will always work.