Why Is My Fresh Water Tank Losing Water While Driving?

[SKIPPERUPS]

Can anyone explain why my 2025 Montana High Country 295RL losses 2/3rd's of it's fresh water tank capacity while traveling. Water loss is noticeable in rear view mirror while traveling through curves. Water loss is occurring through top of tank due to sloshing. What am I missing here? Thanks in advance for any helpful comments

 

[JFlightRisk]

Very common across all brands and models lately. You have a very shallow tank that sloshes continuously while travelling. The overflow line attaches on the tank side near the top of the tank. Some water gets into the overflow line and the air passing the hose end creates a suction pulling that water out of the line. The fuller the water level the more that will be near the overflow fitting. Note, there's nothing sticking into the tank to cause an actual siphon. It's just the nature of the wide and very shallow tank design. I've seen several spraying water going down the highway.

Many folks have added a shutoff valve (as we did) to the end of the hose however you then need to remember to open it while filling the tank, close for travel, and reopen to use the water pump so the tank doesn't collapse.

 

[SKIPPERUPS]

Thank you JFlightRisk. This information is very helpful

 

[JFlightRisk]

Glad to help. It's been a common issue since the manufacturers decided to put freshwater tanks underneath RVs, perhaps to lower the center of gravity or make more storage available inside by taking them out from underneath the bed like our '96 Wilderness had.

 

[baybum10]

My tank had a crack across the top. When traveling the crack would open up and water would slosh out. Back then it was a common problem and the tank was replaced under warranty.

 

[rickybobby]

My 2017 has the fill/vent in the rear, I whittled a stick to fit the hole. After filling, I insert it and pull it out upon arrival. No more water loss.

 

[danaw]

I remove the cover and screen and plug the vent with a boat plug. Works great. I also tape a note over the pump switch so I remember to remove the plug avoiding collapsing the fresh water tank.