I installed a new gowesty propane tank on our vanagon.

I'm having trouble finding someone local to "purge" the tank before filling.

One idea I had was to have the local filler put in a half gallon, and then
vent gas out of the bleeder valve for 20 seconds or so, and then fill the
rest of the way.

I imagine this would exhaust the vast majority of the air in the cylinder,
since the propane will be evaporating and trying to displace as much
existing gas as possible.

Thoughts?

Thanks!
-Wes