Wednesday, November 30, 2022


Avoid fresh water contamination from nasty waste water


By Russ and Tiña De Maris
The occasional letter brightens up our day and stimulates the “little gray cells.” Here we go with one on holding tanks:

Dear RV Travel:
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 L.

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.

What is 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 RV.

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 can prevent this from happening?

Inexpensive backflow preventer

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.


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Dr. Mike
1 year ago

I would like to ask two follow-up questions to Russ and the rest of the audience:
How long do you keep water in the freshwater tank? If you put the coach in storage for a month, would you drain the tank or just top off before the next trip?

Second question: How often should the freshwater tank be sanitized?

Note: We usually do not drink the freshwater, but use it for showers, hand washing, and toilets.

Randall Rosebrock
1 year ago

As I read, the thought occurred to me, shouldn’t there be two hoses? Preferably one green for fresh and one yellow for wastewater. It’s all good and fine to have a backflow preventer but shouldn’t the backflow be at the end of the hose so it never gets into the hose? Even when that is done there is a minuscule percent of wastewater at rv connecter and backflow relies on coming back into the hose to close the valve.
In my thinking 1. You should have two hoses one green and one yellow. 2. Backflow preventer should be at the output end of your green hose!
just thinking…..

Frank D
1 year ago

I think you mis-understood the question. “My husband is a neat-freak. He can’t stand to think about the stuff that lives in our RV holding tanks, and thinks that he needs to flush the tanks clean as a whistle every time we get home from an RV trip.”

Cleaning your Grey & Black tanks is a must to keep your “level sensors” operating. There is usually a line at the dump station and people have a tendency to rush the dump. Struvite will build up in both your Grey and Black tanks, because of what it contains, so, “Pereiodic” deep cleaning is needed.

Here is an excellent video with a excellent explanation on cleanliness from the RVgeeks.

martin a
1 year ago

Many campgrounds require a backflow prevention device to protect their water system which may be a well or public system.

1 year ago

It just amazes us that folks use the hose at the dump station (which clearly states it’s not drinking water) to fill their holding tanks when arriving at the campground and also water jugs!! We watched three campers do this just last week.

Paul S Goldberg
1 year ago

In addition to the backflow preventer, which with a built in sprayer is part of the system, one should NEVER use the potable water supply hose for anything other than potable water supply. I carry a green garden hose for all other water uses including washing the coach and flushing the black and grey tanks. Since we are full time I do not worry about getting tanks clean since they are “contaminated” almost immediately. I just try to get all the solids flushed out of the black tank.

Ron T.
1 year ago

A backflow preventer might make her husband feel better, but I fail to see how it’s going to keep him from driving her nuts . . .

1 year ago

To me that is another one of the items that should be standard equipment on an RV, along with a water pressure regulator and surge protector. Maybe they are on some newer, better models.

1 year ago
Reply to  Dan

Most trailers with built in black tank flushes will have a back flow preventer installed in-line. Problem is it’s usually hidden in the wall or under a sink and they are prone to fail and flood your rig. I’m going to remove mine and hard pipe the connection, then use one on the inlet port outside instead. Too many reports of the in-wall factory ones leaking!

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