Today we are going to talk about RV retention tanks. To start with, I wanted to mention something about RV retention tanks that I don’t think many RVers are aware of. Many of the free dump stations available to RVers are closing due to chemicals that are harmful to septic systems and because RVers are abusing these dump stations. If we want to have access to these dump stations, it is absolutely essential that we use safe septic chemicals (no formaldehyde), and that we clean up the trash and do not abuse the dump stations.

Your RV has what is known as a gray water holding tank and a black water holding tank. The gray water holding tank collects dirty water from the kitchen sink, bathroom sink, and shower. The sewage holding tank is for the toilet. These tanks end in a main outlet used to empty the holding tanks. This is where we connect our sewer hose.

Make sure you have the necessary couplings and connectors. It may be necessary to join two hoses to reach the sewer connection. I recommend that you only use heavy duty sewer hoses. They are not that expensive and they hold up much better. Have a 10 foot hose and a 20 foot hose available. Do not drop or drag the sewer hose on the ground. This will cause it to break or form holes.

To connect the sewer hose, make sure both valves are closed and remove the sewer cap. Make the connection by placing the hose adapter over the outlet and turning it clockwise until it snaps into place. Run the other end of the hose to the camp sewer connection. Use the necessary adapters to make the connection and obtain a good seal. It’s a good idea to put some weight on the hose so it doesn’t pop out when you drain the tanks. It may be necessary to use some type of sewer hose bracket to get a good angle from the RV to the campground sewer connection so that the tanks drain properly when you empty them. The small valve is for the gray water tank and the large valve is for the black water tank.

A rule of thumb for RV storage tanks is to never dump the sewage tank until it is at least two-thirds full. You want the tank to be almost full so that the weight and gravity force the contents of the tank to drain properly. Another rule of thumb is to never leave the valve on the black tank open at camp and wait for the toilet to drain or flush like your home toilet. It will not work.

When tanks are full, or almost full, always empty the black tank first, followed by the gray tank. The gray water tank must also be at least two-thirds full. Emptying the gray water tank last will help remove the sewer hose.

When camping for an extended period of time, you can leave the valve on the gray tank partially open to drain while using it, but remember to NEVER do this with the black tank. If it’s time to leave camp and your storage tanks aren’t full, you can finish filling them with water and then throw them out. Never use your potable water hose for tank maintenance or cleaning. Recreational vehicle drinking hoses are typically white. Take a different colored hose for other uses so you can tell the difference.

After emptying the tanks, you must clean them thoroughly. Some RVs have a built-in system for unloading the tanks. If not, there are other ways to do it. You can use a tank wand designed to clean and rinse the black tank. The only problem is, you don’t know when or if the black tank is really clean and you can’t rinse or clean the gray tank with a wand. I use a product called Flush King. It is a reverse flush valve that connects directly to your sewer outlet and flushes and cleans both holding tanks in one operation. It’s easy to use and has a clear barrel so you know when the tanks are really clean.

Every time you dump the black tank, you should treat it with holding tank chemicals to help control odors and break down solids. You should always use environmentally safe chemicals. Enzyme-based chemicals use good bacteria to digest waste and control odors. Formaldehyde-based chemicals destroy bacteria needed to break down waste and can be dangerous to humans and pets.

The first step is to add enough water to completely cover the bottom of the tank. Four or five full toilets should be sufficient depending on the size of your black tank. The water will go a long way in controlling the storage tank odors. You always want the contents of the tank to be covered by water. Next, fill the toilet bowl and add the proper amount of chemicals to the storage tank, usually four ounces for every forty gallons in the tank. Unload the bathroom. Repeat this procedure each time the sewage holding tank is emptied. Some holding tank chemicals, such as RV Trine, also contain valve lubricants to keep valves working properly and extend the life of valve seals.

You should always use toilet paper designed for use in RVs. This toilet paper breaks down and dissolves in the holding tank chemicals, preventing potential problems with the holding tank, RV sewer system, and flush station septic system.

False storage tank readings on the monitor panel are due to the storage tank probes being covered by toilet paper or other debris. If washing the tank doesn’t solve the problem, add a little water and a couple of bags of ice cubes to the empty storage tank. Drive or tow the trailer so the ice cubes can scrub the sides of the tank. Proper storage tank chemicals will also keep the storage tank probes clean.

Over time, grease and debris builds up in the gray tank and causes a bad odor, not to mention how it’s affecting the tank and the valve assembly. Periodically treat the gray tank with environmentally safe holding tank chemicals to avoid tank odors. When the tank is empty, you can also add a little dishwashing liquid down the drains to help break down grease and residue buildup.

By following these simple holding tank tips, you can avoid problems and provide long-lasting, trouble-free storage tanks. This is a problem that we can all do without! All of our RV tour videos cover information on RV storage tanks, water system, LP gas system, electrical system, and more. Take a look at our new “VR Essentials” DVD to show you what items you’ll want for your RV to make all of your VR experiences more enjoyable.

Happy Camping,

Mark J. Polk

Copyright 2006 by Mark J. Polk Owner of RV Education 101

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