"David A. Webb" wrote in message
...
Is it simply to remove air because the air may contain moisture?

I had this done (for free) with two new tanks (20lb) that I purchased. The
guy doing stated that if the moisture is not purged from the tank, then the
valve may freeze up when in use. This would kill any output from the tank.

I filled mine at a Flying J gas plaza. I have also had good luck using
smaller mom/pop places like the local feed mill and a small one man used
trailer business. I realize that the 100lb probably needs to be filled by a
truck coming to you, but what the hey ...