For a better rest, use a backflow preventer


By Russ and Tiña De Maris

The occasional letter brightens up our day and stimulates the “little gray cells.” Here we go:

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 iPod headset to the 30-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.

pukeWhat 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 let 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 and easy to use. Here’s an affordable one. Use them and rest easier.

##RVT768 ##RVDT1248

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Shawn Rosvold
5 months ago

Great info. Had to Google hose bib. Never heard that one before.

9 months ago

The problem we had with installing a backflow preventer like the one shown in the article, we wanted something at the inlet to the rv so that when the campground water was shut off (it happens here) we could use the onboard tank with the water pump; the problem was that the water pump just pumped the water out the little holes on the valve. I guess what we need is some kind of one way valve there.

1 year ago

The Amazon link leads to a “Vacuum Breaker” not the “Backflow Preventer”. The BP is shown further down the Amazon page FYI.

RV Staff (@rvstaff)
1 year ago
Reply to  WEB

Thanks, WEB. I’ve changed the link to a “backflow preventer/vacuum breaker” — and it looks about the same to me as what we had linked. But we’ll play it safe and cover all of the bases. 😀 —Diane at

Steve S.
1 year ago

I disagree as to where the backflow preventer is installed as described in the article. The article says to install it between the hose bib and the hose. If installed this way, in a backflow situation, the hose itself would become ‘contaminated’. The entire interior of the hose would need to be sanitized because after all, who knows exactly how far the contaminated water back flowed? My opinion is that the backflow preventer gets installed as close to the source of ‘contaminated’ water as possible. In this case, it would be installed between the hose (male end) and the cleaning device. This way, if there is a problem of some sort, there would be no contaminated water flowing back into the hose itself. If there is some sort of ‘overspray’ of contaminated water, it is a simple matter to sanitize the exterior of the hose that was sprayed. Plus, if you really wanted to be safe, sanitizing the last foot or so of the hose nearest the contamination (inside and out) is much easier than having to sanitize the entire interior of the hose.

Roy Ellithorpe
4 years ago

The black tank flush on my Travel Supreme seemed to be plugged as very little water sprayed into the tank (going by the sound and the fact that I couldn’t get it to stop leaking at the hose connection). Over the years we have also noticed a sewer smell in the bathroom area at times.
When I had it apart for another reason, I noticed that it had a loop that went up through the floor and into the cabinet under the sink. At the top of this loop was a vacuum breaker type valve. I couldn’t understand what the heck that would be for, so I ripped it all out and ran the line straight from the inlet to the flusher. Now I have lots of pressure on my flusher and no leaks. We haven’t used it enough to know whether the smell is gone but are hopeful.
Can you please tell me what that was all about and why I shouldn’t have removed it?

1 year ago
Reply to  Russ De Maris

The “air gap” valve is for the gray tank and has nothing to do with the black tank. It allows the gray tank to drain while not allowing water in the P-traps to be sucked out. The device that Roy removed is the anti-syphon valve that is essentially a back flow preventer. Removing it will possibly allow contaminated black tank liquids to be sucked back into the garden hose when the water pressure is removed. Conditions have to be just right for this to happen, but it can. My recommendation is for Roy to replace that valve with a new brass one that can be found at Home Depot or other hardware stores and even on Amazon.

Nixk DiPietro
4 years ago

Your articles are very informative and edgucational. You take the mystery out of alot of different problems one may encounter RVing. I for one enjoy reading them very much. Keep up the vood work.
Nick DiPietro.