I've done a few and my usual method is to first rinse with water then
attach a shop vac to the gas fill opening (using the handyman's secret
weapon). Have the vac running while welding. The first time I tried
this I remotely started the vac to be sure fumes would not ignite in
the vac.

Modat22 wrote:
I need to make sure it won't explode and was thinking about letting it
sit in the sun open for a few days then fill it completely with water.

Any other ideas?