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Maintaining Holding Tanks

During the past several weeks, I have been writing largely about RV plumbing systems. In this two-part article, I will continue this theme and present some methods of maintaining and cleaning holding tanks, as well as how to resolve incorrect tank level readings.

Not all RV owners are aware of the correct way to manage holding tanks. It is very important to maintain a level of liquid waste in the black water tank in order to avoid the solid waste drying up in the tank. By way of introduction to this week’s topic, let’s examine the recommended method for holding tank operation. Although this technique is quite well understood by many, it is worth reviewing, as it’s the best way to minimize the chances of solid waste sedimentation.

Dump Station SignWhenever possible, refrain from dumping your holding tanks until the black water tank is at least 2/3 full. This will allow for the greatest chance of a full drain due to the large vortex created by such a large volume of liquid. Be sure to dump the black water first, then the gray, which will help rinse the drain hose. If you stay connected to the park sewer connection during camping, do not leave the black tank valve open. Doing so will allow the liquid waste to drain, while the solid waste may attach itself to the bottom of the tank instead of going down the drain. If left long enough, the waste will solidify and may not loosen and refloat when it is eventually exposed to liquid again. Sediment waste, although not desirable, often does not cause a problem in the holding tank unless it is allowed to accumulate further, possibly leading to clogging or level indicator errors. In any case, it is best to avoid it.

Many RV’s use well nuts to monitor tank fluid level. Well nuts are simply metal probes that stick into the tank to measure liquid level. Since they protrude into the tank, they can become clogged with waste, toilet tissue, and the like, which can cause level misreading.

RV-bathroomIf you suspect your tank level gauges are not reading accurately, there are a few simple tricks you can try. The first is simply to flush the tank several times. If your coach is equipped with a built-in flushing fixture, open the tank drain valve and run water through the tank flush fitting for several minutes. If you don’t have such a fitting, purchase an RV holding tank flushing wand and use it to clean the tank. Allow the water to run for several minutes. Once either of these operations is complete, check the level readings to see whether the tank level shows as empty. It is of paramount importance that the tank drain valve be left open during these procedures!

If these steps don’t work, add water to the black tank through the toilet until the tank is at flood level. This means that water should appear above the toilet flush valve. Open the black tank drain valve and drain the tank. Do this several times. The large suction effect caused by the large volume of water will dislodge much of the debris stuck in the tank.

The final trick is to pour a full bag of ice into the holding tank through the toilet. Add several gallons of water and drive the RV around until the ice melts. The ice cubes will loosen much of the waste and debris accumulated on the tank and probe surfaces.

In next week’s article I will discuss tank blockages and how to clear them.

About the Author: 

Steve Froese, an avid RV owner, traveler, and Coach-Net member since 2013, is the principal of “A Word to the Wise Technical Communications”, a published RV author, certified RV technician, and licensed Professional Engineer. He frequently collaborates with the “RV Doctor”, Gary Bunzer, and has worked with the RVIA/RVDA as a technical and training writer and consultant. Professionally, he works as a quality engineer and musician. Watch for more of Steve’s work in upcoming Coach-Net publications.

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