Even if you own a high-end coach like a Newell, Foretravel, or Country Coach and it has a sewer tank flush, it is a good idea to occasionally give the tanks a manual clean out if your built-in flusher is just a sprayer and not a hose inside the tank. If your sprayer is the kind with a hose inside the tank, you should be able to hear it flopping around when in use; however, those sprayers were known to blow the hoses off into the tank.
I start with an empty tank. Partially fill the tank with 4 or 5 toilet flushes. (Full toilet). Add dish soap or laundry soap with about a quart of bleach or a bottle of Pine-sol. Let it sit for an hour. I use a thin-walled (cheap) 1/2 inch diameter garden hose which has the end cut off. I cut a piece of thin flat plastic and wedged it into the cut-off end of the hose so that the end was stretched. This turned the hose into a sprayer, and with the high pressure where I get my water, after removing my in-line regulator, this hose flopped around like a cat whose tail got caught under the rocking chair. Anything stuck into the end of the hose will work as long as it stretches the end and doesn’t completely cut off water flow. You can experiment with it before putting it to work. What you want is for the hose to flip and flop around a lot (like our politicians). You are not going to use this hose for anything else other than this job.
Feed this hose down the toilet and turn it on full force. You may need to place a wedge into the toilet to keep the flap from collapsing the hose but make sure that whatever object you choose for this job is too large to go down the toilet. You should be able to hear the hose flopping around inside the tank. It
will spray into most of the places the built-in sprayer can't reach, which may include the probes for the monitor panel. On units that have multiple probes screwed into the side of the tank, these probes tend to collect toilet paper on them and makes the monitor panel read the tank level incorrectly. Now go out and open the dump valve…this is CRITICAL! Don’t let it go too long, or your tank will fill up, and the commode will overflow. That initial blast will blow your soapy solution up on the walls, and inner roof of the tank, helping dislodge solids. Leave the dump valve open and the hose spraying for 10 or 15 minutes but do not leave it unattended. The hose could creep back up out of the toilet. I have a clear sewer hose adapte that connects my sewer hose to the dump valve so I can see how clear the water is coming out of the tank. I quit when I no longer see any solids or discoloration of the exiting water. When doing this clean-out, wear disposable gloves because you will have to handle the hose when you remove it from the toilet. Wipe the hose with cleaner disinfectant and put it in a marked plastic bag for re-use.
Nothing on earth is going to make the sewer tank smell good but you will have fewer aromatic surprises when you flush your toilet after the clean out. I advise a monthly clean out in summer and using the built-in sprayer each dump. About every other month in cooler weather but you really can’t do it TOO often.
Editor's Note: To learn even more about properly cleaning your RV's Black Water tank you may want to take a look at the video below by RVing Expert Mark Polk from RV Education 101
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