I have had hundreds of bottles filled, and only once was a scale used to do it. That was at a place in Canada. Everyone else fills it using the bleed valve to indicate full, the more cavalier operators let the pump run until the OPD float cuts it off but even then they have the bleed valve open.
A friend of mine (a fireman) used to refill the little disposable tanks to save money. One time he had one in a tote sitting out in the sun and it blew with a huge bang, throwing debris in every direction 50 yards or so.
