Avoid yucky problems with this dumping technique


RV Staff Report

When you have full hookups, leave both the black and gray water valves closed. This allows solids and tissues to start breaking down and liquefying so they will flow better.

When your black tank is about half full, empty it followed by a good flush from your gray tank. The gray water will thoroughly clean out your dump hose.

sewer hose slinkyWhen you leave the valves open you are likely to have bad odors, create a build-up just below your toilet discharge valve, accumulated waste will collect in your dump hose causing even more odors, and un-flushed matter will collect on the bottom of your holding tank and harden becoming almost impossible to clean out.

Use a board or commercial product (like the Slinky shown in the photo) to lay your hose on that will maintain a slant between your hose outlet and the dump station to create a better gravity flow and no low spots where waste will collect.


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re: filling black tank to full
My experience as well as others is that after the FULL light comes on at your control panel [if it works], most people push it a few miles further down the road and end up really full.
Leaving a 2″ air gap will not affect the dump but might help your state of mind vs some drain flushing up.
Bare with me. From my diving days, one atmosphere salt water = 14.7psi = 33 feet depth [aprox 0.5 PSI/foot]
Guessing my waste tank liquid is 2x denser, that equates to 0.08 PSI per inch. I am thinking that leaving a 2″ air gap will not become a dump problem.


I installed a 3rd gate at the junction of the drain pipe and connection of the stinky slinky. This allows me to dump the black tank first (while the black tank flush is running), then close all three gates. I then open the gray tank and then the black tank keeping the 3rd valve closed. This will allow the soapy gray water to partially fill the black tank. Once the two tanks have equalized, I then close the gray and open the 3rd gate…..dumping the black tank once again. I can do this two or three times (depending upon how much gray water I have) and keep a little extra to flush the stinky slinky. This procedure has kept my black tank free of any sludge and operating correctly. I never use any chemical, just plain water and a little liquid laundry soap when traveling. No odors, no sensor problems, and no flushing problems.

Michael Allen

I don’t empty the black tanks (i have two) until they are 3/4 full. I flush the tanks each time I empty and I generally run the flush twice. As for the grey tanks (two also), I open the master bath tank when I take a shower and close it after I’m done. Since I have on-demand hot water this allows me to take as long a shower as I want. I always empty the grey tanks after finishing flushing the blacks. So far, no problems after 15,000 miles.


All well and good…UNTIL you run into a park where the sewer is UP HILL from the discharge valve…like where we are now. I think we’re going to have to use our macerator to get this to work.

Abe Loughin

I agree with most of the information given in this tip. However, I have learned that waiting for the black tank to be full or nearly full and using proper chemicals allows for the solids to break down better and the extra gravitational pressure carries any remaining solids out better. Also flushing the black tank is recommended.

Gary Bogart

I did one better and installed a tee in the shower hot line and a 1/2 inch pex return line to a 12 volt valve connected to a non pressure line before the pump. Cost with do it yourself labor less than $35.00
Everthing is hidden. To control the 12volt valve, I connected it to a momentary switch off the pump circuit. Hold the switch for a count to 10 and hot water.