Monday, March 27, 2023


Losing water from fresh tank vent on steep grades?


Here’s a question from a reader of about boondocking. 

Hello Bob,
You gave me some great advice a few months ago when I asked about boondocking during our trip from FL to CA. We had a GREAT time! Now, here is a question for a situation that came up during that trip.

We have a 30-gallon fresh water holding tank on our Class C. We were diligent about filling it up before each day’s new adventure. Problem is, while driving up the steep hills and mountains, we would lose water out of the overflow drain. My husband used a small carrot to plug it, but that got old (and so did the carrot!!). Is there a simple fix? Maybe a cap specifically designed for that purpose? Thank you! —“Friskie” 
Hi Friskie,
You’re not the only one to experience losing water from your fresh tank on the steep grades of the Western mountains – including me. I have a 100-gallon tank and didn’t think that I lost a great percentage of the water. However, with smaller tanks, it could be enough loss that you could  run short.

The ideal fix would be for manufacturers to put the air vent (where the tank overflows) at the top of a tube extending up from the top of the tank a foot or so. This would prevent overflow. Maybe there is a code that prevents that factory modification.

I have heard of RVers both temporarily plugging the hole while driving on steep terrain and affixing their own tube into the vent hole and plugging the top with a tight fitting cap. In both instances don’t forget to remove the restriction when you set up camp. Your carrot (or a zucchini) would work also. I would suggest that you contact your RV manufacturer’s support page and ask how to stop the overflow and see if they have come up with a fix or a solution. 

Read more about boondocking at my BoondockBob’s Blog.
Check out my Kindle e-books about boondocking at Amazon.

Do you have a question for Bob? Email him at bob.rvtravel (at) .





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robert maher
5 years ago

I am sure that there is a check valve that is one way, that would let air in and not water out just like the diodes that we use on the lights when we tow. our car.

Greg Illes
5 years ago


I had this problem and it was severe. For my configuration in my motorhome, a complete re-do of the vent system was required (and possible). Not for everybody, but handy folks may be able to make use of some ideas. Here is the link on rvtravel:


Don Schneider
5 years ago

We have 2 overflows on our Fresh Water Tank. I went to the hardware store and bought 2 shutoff valves. They are installed in the vent lines and I turn them off while traveling and back on when setup.
This was a cheap alternative and parts are readily available.

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