In article ,
David A. Webb wrote:

My initial statement was based on the fact that there was liquid LP
(I know it is redundant) and any tiny bit of air that might have been
in the tank with the liquid would have been purged when I vented the
tanks.

Once the liquid was evaporated, and the pressure inside the tank
dropped to zero, it is safe to assume the only thing left in the tank
is LP vapor.

If you let the LP vapor bubble out thru a jug of water, if there is any
suck back it will be water.

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