RV Holding Tank Questions and Answers, Part 1

Our question-and-answer sessions at RV rallies are always the most popular and a great way for us to close out our seminars. Here’s the first in a new series. Keep an eye out for more Q&As in the coming weeks.

Q. What happens when I overfill my tanks?
A. Well, if you are lucky, any overfill in your black or gray tank will travel up your vent pipe and make a mess on the roof. However, the answer is a bit tricky and depends on the exact plumbing setup of your RV. Some RVs have back-check valves built into the plumbing system, preventing waste from backing up into the shower or tub, toilet bowl, or sink. This is normally a feature of higher-end RVs, so most of us aren’t that lucky.

For most RVs, gray tank overfill will back up to the lowest point, which is usually the shower. How many of us have taken a shower only to look down and see the water rising? Yep, you waited too long to dump that gray tank! In the black tank, there’s a higher probability that waste will travel up the vent pipe, but we have also seen it back up into the toilet (talk about a mess!).

In the worst case, waste can burst your tank(s), making a mess everywhere and very expensive repair. It’s always best to monitor your tank sensors (or whatever method you use) and dump those tanks on a regular basis.

Q. How often should I dump my tanks?
A. The plain answer is, when they are full. Your RV’s holding tanks are large, squarish boxes. The more volume in them, the better they drain out and carry any waste out through the drain pipe. A fuller tank provides more down pressure, resulting in the familiar swirl or vortex you see in your home toilet. That swirling water helps to clean your tanks.

If your tank isn’t full (according to the sensors or whatever method you use) and it’s time to empty them (perhaps you are leaving your RV park or you just want to empty them), add extra water, either down the toilet (for the black tank) or shower or sink (for the gray). Try to get them 80% to 100% full.

Q. Does my RV’s onboard tank flush do anything?
A. In almost every RV, the black tank has an internal spray nozzle that spurts out water into the tank. Water is supplied to this spray or flush system via a garden hose that attaches to the RV park’s water supply at your site and then to a garden hose fitting on your RV. Some RVs (like Country Coaches) have a similar system in the gray tank (this is not common).

Some models have a rotating nozzle, though most are a simple spray head, located at either the back or top of the tank. Most manufacturers (and dealers) will say that this flush system is all that is needed to keep your tank clean. We tend to disagree, though the system does have some benefits.

For one thing, it’s better than nothing. The spray nozzle tends to spurt water in a set pattern at about 100 to 150 PSI (depends on the park water pressure, size of the nozzle hole, and whether the hole is stopped up (more on that later)).

Does it do a complete job of keeping your holding tank clean? No. But it can help to “move things along” when you use it during normal emptying of the tank (something we recommend).

If over time, you don’t think the spray system is working anymore or the amount of spray is lessening, it probably has some corrosion at the spray head. Take some CLR, our about a cup down the empty garden hose, connect it to your RV’s flush system input, and quickly turn on and off the water, driving the CLR to the nozzle head (just a few seconds is all that is needed). Let this “sit” in the system for a half hour them flush the system out (and empty your tank — that CLR is super bad for soft rubber seals).

Q. Can you put bleach in your RV holding tanks?
A. Household bleach is a dilute solution of sodium hypochlorite (NaClO) and other secondary ingredients. As we know, it’s commonly used as a cleaning and disinfecting agent around the house and even RV. Chlorine, the “Cl” in the molecular formula, is a powerful oxidizer.

While many RVers use bleach to sanitize their fresh water tanks (and that’s fine, as long as you don’t let it sit in your waste tanks too long), using it directly in your black and gray holding tank is probably not a good idea. That bleach can damage soft rubber and plastic parts in your seals and gate valves, something you should try to avoid. If you are looking for a safer alternative, try our RV Tank Solution recipe.

Jim Tome, Owner

Jim Tome, Owner

Hi, I'm Jim Tome and, along with my wife, Debbie, the owners of Kleen Tank LLC, the national leader in RV holding tank cleaning service. We've been RVers like you since 2004 and have traveled all over the U.S. in our Airstream travel trailer. We started the business about twelve years ago and have cleaned tens of thousands holding tanks in thousands of RVs. From tiny weekend travel trailers to monstrous fifth wheels to luxurious motorhomes, I've seen just about every situation there is with RV holding tanks and waste systems. I hope you enjoy our articles; I try to post at least one per week and we've got a great library of them to cover just about every problem. Enjoy!


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