Propane valve

Question for my own curiosity.
I have (2) 40# propane bottle in the '12 Key Largo. If I fill one of the bottles and the other is almost empty...turn the selector valve to the middle position so both tanks are connected to supply....do the tanks:
(a) Equalize?
(b) draw from the fullest (or emptiest) tank?
(c) draw equally and therefore eventually empty the almost empty tank?
(d) ?

Thank you!
Retired and travelling since April '16.
Loving the RV lifestyle.
'12 RAM 3500
'12 Landmark Key Largo
DW Linda
Kitty Joy


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