By Greg Illes
It’s surprising at times how much impact a simple oversight can be. In our Itasca motorhome, the fresh water tank had a factory-installed venting tube. This is a necessary feature so that the tank can “breathe” with capacity and altitude changes. However, the way the designers chose to install this vent was not ideal.
The vent was routed immediately out of the tank and down below the RV floor. Consequently, normal driving would slosh our fresh water out of the vent. On one occasion, we arrived after a long winding road at our destination with nearly 30 percent of our water already spilled overboard!
This venting style is not uncommon, especially if you have dual-fill capability (gravity tube and city-water connections). So it’s a really good idea to check the design of your venting system and make corrections if necessary.
If your venting system is designed with an uphill vent like the top image in the diagram, you’re probably in good shape to keep all of your water in the tank. But if you have venting which goes immediately downhill, your fresh water will spill out on turns, slopes, and the typical jostling which accompanies motoring down the road.
If your venting system is a wasteful one, the fix is fairly easy. You can interrupt your vent line and make it much more difficult for the water to exit. CAUTION: Don’t think about simply capping it off — that would result in tank collapse or rupture. Always make modifications with equal-diameter tubing. And always be sure any changes you make leave the vent clear and unobstructed.
The two basic fixes are to either rerun the vent uphill (for example, to where the gravity fill entrance is), or to make a racetrack of tubing around the top of the tank before exiting downwards. Either method will prevent or drastically reduce water spillage. A variation would be to run tubing upward a couple of feet and then back down again (no, this will not cause a siphoning action).
Every installation is different, so it takes some study of your available space and maybe some experimentation. But if you’re losing precious water, it’s definitely worth the trouble and a few bucks’ worth of tubing.
Greg Illes is a retired systems engineer who loves thinking up RV upgrades and modifications. When he’s not working on his motorhome, he’s traveling in it. You can follow his blog at www.divver-city.com/blog.