Newly-filled Propane Tanks empty in four days-not used much

This discussion is very interesting. I was told that when they refill a propane tank it is never filled completely; there is always room left for some air. Is this correct? Also that you should regularly bleed your propane tanks of air until a white mist starts coming out. Don’t know if that’s correct either?

Thought I’d mention that I put a small lock on both my propane tanks because I have heard of people stealing propane tanks off an RV while the owner is sleeping or away from their campsite.