Originally Posted by dcrajr
I have exactly the same issue with my 33ik. I am having a shut off value installed and hopefully help with the issue. I have read other threads that suggest that there is no need to open the value until you are ready to re-fill the tank. So... I am wondering who is correct on the issue of having to open the value after using a bit of water or just keeping it closed? What function does the vent line play after filling the tank?
2010 GMC 2500HD 6.6 Duramax Diesel
Pullrite Superglide #2900 ISR Hitch
2021 CC Silverback 33ik
It allows water to be used from the tank without sucking the tank sides in.... IF...IF... the system doesn't have some other method of venting. (like a hole in the fill cap for instance)
Every fresh water tank system and fill method is somewhat different. Not only in the physical parts but also in how well (or not) they are plumbed.
Some units seem to siphon out the vent hose where others don't when plumbed similarly.
The vent serves TWO purposes... it allows the air to escape the tank when filling while also allowing water out of the tank once full. This is especially important on R/Vs that use the city water hose to fill the tank as opposed to a gravity fill where some air can escape via the gravity fill tube. Without an overflow, you could possibly fill the tank until it exploded or (as we have had reports of) it will bulge the tank and bust the floor or the tank supports. It is never a good idea to "blast' water into the tank faster than the air/water can escape out the vent.
Secondly, the vent allows the water to be used out of the tank and allows atmosphere (air) back in the tank so there isn't a vacuum sucking the sides of the tank in as the water is removed.
Both of these scenarios require everything to work correctly and most times because of poor routing, kinks or poor connections, none of it works quite the way it should.