Originally Posted by blderman
It siphons out of the overflow tubes. The other trailers I owned did not have these tubes so I am not sure why Jayco thinks it's necessary.
From my Note 5
With your elite model, I believe you have a 2nd FW tank for greater FW capacity. The vents are needed because of the way the two FW tanks are tied together to equalize the water level between the two. The gravity fill goes just into the first tank. That tank can expel some air via the gravity fill or vent that ties to the gravity fill. If you fill too fast, you will get burping as the air tries to escape via the same route that the water is going in.
But the second tank only gets filled by a 1.5 or 2 inch hose that connects to the first tank and equalizes the water levels between the two. Once the first tank gets a couple inches of water in it, that equalization hose is completely under water and there is no way for the air in the second tank to escape. So the overflow tubes also act as a vent for the second tank, letting the air escape so the water can enter via the equalization tube. Same thing happens when you turn on your pump and draw water out of the tanks. Without the overflow/vent tube on the second tank, you will be creating a vacuum if air can't get back into the tank.
That's why it is important if you put a shut off on the tubes to always have it open when filling and when drawing water out.