What You Need to Know About RV Holding Tanks

Updated on January 17, 2019
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Just a guy with an aptitude for many things mechanical, electrical, and electronic who has been building and fixing things for 40+ years.

The Basics of RV Holding Tanks

When you own an RV of any type, it is important that you understand how the various systems work so you can use and maintain them properly. This article will explain the basics of your RV's holding tanks. The picture below illustrates a typical RV plumbing system.

Your RV will have three types of holding tanks: fresh water, gray water, and black water. Larger RV's may have more than one of any type of tank. For example, very large RV's that have a bathroom in the front and rear will probably have two blackwater tanks, one below each bathroom.

Typical RV Plumbing System

The Fresh Water Holding Tank

The fresh water holding tank supplies to the bathroom and kitchen faucets. It is also the water that is used to flush the toilet(s). If your RV has an outside shower, the fresh water tank will supply that as well.

The fresh water tank can also supply your drinking water, but if so you must be diligent about sanitizing your fresh water tank. Personally, I would rather not worry about sanitizing the fresh water tank and taking the risk of drinking contaminated water. We bring our own drinking water in bottles. I bring cases of bottled water for drinking, plus a few one-gallon bottles that I fill with tap water at home to use for the dogs. We use water from the faucets only for hand washing, showering, and washing dishes.

Even if you never plan to drink from the fresh water tank, you should NEVER put anything except potable water into it. Potable water means that it is water that is safe to drink. This is water that's available from the hose bib or faucets at your house or from a potable water source at a campground or dumping station. Many, but not all, dump stations will have potable water available. It will be a separate hose that is a distance away from the sewer part of the dump station. Make sure it is clearly marked as potable water.

NEVER fill your fresh water tank with the hose that is at the dump area. That hose is used to rinse out the sewer hose and fittings for your RV, and it comes into contact with all the nasty stuff in the sewer hose and fittings.

The Grey Water Holding Tank

The gray water tank holds the water that goes down the sink and bathtub drains. This water is mostly just water, soap, and whatever you wash off your dishes and hands. The grey water tank does not typically emit an odor, so there is no need to use a deodorizer in this tank. However, some people will use a deodorizer in this tank anyway.

Another article will go into the details of emptying your holding tanks but for now, just note that you should empty the gray water holding tank AFTER you empty the black water holding tank. The reason is that the grey water rinses the black water out of the hose and fittings. After all, the gray water is mostly just water and soap.

The Black Water Holding Tank

The black water tank is the nasty one that people don't like to think or talk about. This tank contains everything that is flushed down the toilet. Beyond that, I don't think that I really need to go into much more detail. It is not pleasant.

You should use a deodorizer in the blackwater tank. This helps neutralize odors and helps to break down waste which makes it easier to empty the tank. Deodorizers are available in liquid form or packets and are added to the tank via the toilet. The package or bottle will tell you how much to use based on the size of your tanks.

A tip for the blackwater tank is this: Don't skimp on water. You need water to help spread and break down the solid waste.

There are two points of view on this subject, and I've tried both. What I've found is that one works, one doesn't.

The first approach is as stated above; use plenty of water. Pour two or three gallons down the toilet when you first set up and add your deodorizer. After each use, flush for two or three seconds. This gets enough water into the tank to help spread out and break down the solids.

The second approach is to use minimal water when flushing, to conserve fresh water and to delay emptying your black water tank. On the surface, that appears to make sense; in practice, it doesn't work. If you don't use enough water, the solids do not spread out and will form a "pyramid of poo" which will build up high enough to contact the bottom of the toilet and prevent further entry of any other liquids or solids. Your tank indicator may also indicate that the tank is full when in fact it's nowhere near capacity. And trust me on this, when you empty the tank, you will have great difficulty in getting everything out of it.

There is a third approach, I guess, and some people practice it. That approach is to use the toilet in your RV for liquids only and use the campground restroom for the big jobs. I've known some people that don't use their RV toilet at all. It's up to you, of course, but personally I didn't spend thousands of dollars on a travel trailer, so I could trek through the campground in the dark or the cold to use dirty, primitive, remote facilities.

RV Dump Station

It's  tough to take a nice picture of a dump station.
It's tough to take a nice picture of a dump station.

Holding Tank Tips

When you leave on your trip, the gray and black water tanks should be empty. The fresh water tank can be filled before you leave or when you get near your destination. Keep in mind that a gallon of water weighs a little over 8 pounds. If you have a 50-gallon fresh water tank, that's over 400 pounds that you're hauling around. That means that you're going to burn more gas, especially if your trip includes a lot of uphill climbs.

We carry just a few gallons in the fresh water tank when we travel in case we need it during our trip and then fill it up when we get near our destination. It will require some pre-trip research and planning, however, to locate a source of water near your final destination.

For easier emptying of the blackwater tank, use only toilet paper that is made for RV septic systems. It breaks down much more readily than regular toilet paper.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2018 Steve Mark


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