Friday, December 1, 2023


How sewer backflow can get into your fresh water system

By Russ and Tiña De Maris

Dear Go-Go Gurus:
My husband is a neat-freak. He can’t stand to think about the stuff that lives in our motorhome holding tanks, and thinks that he needs to flush the tanks clean as a whistle every time we get home from an RV trip. I say he’s nuts. How can I get him into therapy? —Bea Leegered

Dear Bea:
You could try wiring up his stereo headset to the 50-amp campground outlet for a little electroshock therapy; but, then again, 20-years-to-life is a long time to be away from your motorhome.

Seriously, lots of RVers like having a “Mr. Clean-approved” holding tank, but there is one thing that should be considered before you stick your garden hose anywhere you wouldn’t want to stick your lips: backflow.

Backflow happens when a fresh water system gets “cross-connected” with a source of bad water – or other contaminant. For us as RVers, it’s as simple as a garden hose left in contact with contaminated water, hooked up to the hose bib. Under the right conditions, that water can come back UP the hose, into the hose bib, and into the fresh water lines of the house.

What are the “right conditions” that favor backflow? Let’s say you’re flushing out your holding tank. You’ve got one of those neat “Hydro Flush” systems that lets you hook a garden hose to your holding tank at the same time you’ve got a dump hose hooked up. In the middle of your dump-and-flush operation, the local fire department cruises through your neighborhood, testing fire hydrants. They pull the caps off a nearby hydrant, crack the valve wide open and blast water every which way. Unfortunately, this happens at the same time you’re flushing your tank, and the sudden draw-down in water pressure allows your black water to pulse backwards up the garden hose and right into your house. The same thing could happen if your private water well pump system went on the blink when you’re flushing a tank.

What’s to prevent this from happening? If hubby would buy a commercial tank cleaning system device, chances are the outfit would include a simple backflow preventer to be installed between your hose bib and the garden hose. If a sudden loss of pressure were to set up a “perfect storm” for a backflow, the device would step in and stop the backward flow of fluids, protecting your household drinking water. But oddly, not everyone sees the value of a backflow preventer. Maybe they consider it a nuisance and simply ignore it.

Ignore backflow at your peril. A mouthful of bacteria-laden water can more than ruin your whole day. But black water isn’t the only issue. Consider the harmful effects of pesticides (from using a garden hose sprayer), or automotive antifreeze (from flushing the radiator on the old bus). Backflow preventers are cheap, easy to use, and available at pretty much any hardware store or Amazon. Use them and rest easier.




0 0 votes
Article Rating
Subscribe to comments
Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Oldest Most Voted
Inline Feedbacks
View all comments

Sink Jaxon (@guest_116221)
2 years ago

Meh…what’re the odds?!

Bob Weinfurt (@guest_86126)
3 years ago

I just pour a bucket of water down the toilet after the black tank has drain out to rinse any “nasties” out of the tank.

Sign up for the

RVtravel Newsletter

Sign up and receive 3 FREE RV Checklists: Set-Up, Take-Down and Packing List.