Originally Posted by BarryD0706
Actually two tanks plumbed together like that (and with both turned on) will equalize to have the same level in both tanks.
In theory, that's right, but not actually in practice. The tank that's more full, will have a higher pressure than the tank that's less full. This higher pressure will allow that tank to push more propane into the tee then the other tank. Once the tanks are at equal enough pressure, they will each be able to push roughly 50/50 into the tee and keep relatively at balance.
This works for tanks that were close to each other in the first place. However, if you were to hook up a full tank and a 1/4 full tank, they're not going to equalize to 5/8 each. The full tank will just be able to be used up faster than the 1/4 full, but the 1/4 full will probably run out before the full got down low enough for them to be equal.
Of course I may be wrong, I only have a basic knowledge of how propane works, but my understanding is that the pressure created by liquid turning to gas in tank 1 is insufficient to get the gas in tank 2 to turn back to liquid. And that assumes that the valves are plumbed without any check valves so the propane can flow back into a tank through the outlet instead of through the fill valve.