I have a 92 gallon transfer/auxiliary tank in my 19. I just let it gravity feed but unless you're driving several hundred miles a day or towing for a living I just leave the valve off cause it causes my tank to leak from somewhere on the top when the temperature cools overnight and then expands the next day when it warms.

 

I would start by checking the vent line - is it pinched anywhere? Also probably not related but I think your rollover valve (assuming that is a rollover valve and not just a fitting) is supposed to be on top. From the pics it looks to be on the side.

 

Sounds like you have a venting problem between the two tanks. Don't know your installation but there should be a vent connecting both the main tank and the aux tank just for this reason. Dean

 

What type of aux tank did you install? I’m in the fence whether to install a 62 gal tank or an aux tank.

 

Honestly with the extra work, loss of bed space, plumbing I would do the 62 gallon tank. Then only one tank to fill. Love my S&B tank, only regret I had is waiting as long as I did to do it. Dean

 

I would start by checking the vent line - is it pinched anywhere? Also probably not related but I think your rollover valve (assuming that is a rollover valve and not just a fitting) is supposed to be on top. From the pics it looks to be on the side.

Is there a vent at all? I only see one additional connection along the fill tube. The absence of a vent could explain the problem because if there's nowhere for the displaced air from the main tank to go the tank will pressurize.

 

I installed my 50 gal transfer tank with GPI pump. Plumbed the pump into the fill tube. I ‘tee’d’ the vent/rollover valve into the truck tank vent line just down from where the hose attaches to the fill tube. This will recycle the displaced air in the truck tank to the aux/transfer tank. Just to be sure, I tee’d into that line and ran it to the stake pocket topped either a vented rollover valve. Did a short run to test for leaks. Have to wait a while to do an extended test as I had just filled up.