Abstract: A vapor collection testing device is held in one hand and a fuel dispensing nozzle for a fuel dispensing system to be tested is held in the other hand of an operator. The device is slipped over the spout of the nozzle and pushed against the boot of the nozzle (if so equipped), or otherwise pushed sufficiently over the holes on a bootless nozzle so that the nozzle's flow interlock device is opened. Opening the interlock activates the nozzle's lever, to permit fuel dispensing. Without turning the gasoline dispenser on, the nozzle lever is depressed to open the integral vapor valve. At this point, no gasoline is dispensed, but air is ingested by the nozzle and sent into the gasoline storage tank. The air ingestion can be observed by the device's flow meter, in order to determine if there is a liquid flow blockage in the vapor recovery line of the fuel dispensing system.