Opening bleeder valve while filling until it spews liquid propane out.....proper method
Weighing while filling...proper method
Going by number of gallons clicked off on meter....works but not proper or accurate
Filling until it stops due to activation of Overfill Protective Device (OPD)......wrong method completely. It is a safety device when above procedures have not been followed. Sorta a 'hey stupid' stop filling device.
And there is no air gap..there is a liquid level and vapor area---all propane.
Bleeder valve, OPD and weight are ALL based on 80% liquid level