Propane refilling question

I’ve noticed there seem to be two different procedures to fill my BBQ propane tank, depending on which station I use.

One simply threads the hose, opens the valve and runs a pump until it’s full (I don’t know what signals “full” though).

The other place uses a small screwdriver to open a relief valve near the tank’s main valve. He pumps until a small amount of liquid squirts out, then closes the relief valve and main valve.

My question is why the different methods? Is one method putting more into the tank? There seems to be no noticeable difference in the tank’s weight from either method (but I haven’t weighed it).

I’ve always had the “screwdriver relief valve” method, and assumed it was the proper way. In fact, IIRC there is signage explaining this where I currently get my grill tanks filled. I believe it is to purge any air in the tank.

I’ve always had the valve method, but the tank sits on a scale and when the required weight is reached the valve is closed.

Depending on the outside temp. the temp of the storage tank that the pump is connected to and houw empty the tank is, filling a tank with the vent valve closed can cause the tank to be over filled.

By opening the vent valve while filling when the liquid level reaches the tube conned to the vent valve it indicate the proper liquid level in the tank. With vent valve closed hopefully the tank does not get over pressureized of over filled.