Abstract: A system for safely and efficiently collecting vapors which might otherwise be released during the storage or transfer of a volatile liquid to and from a storage facility. The system includes a collapsible walled receptacle or reservoir which is connected to receive vapors from the storage facility. A compressor or other vapor evacuation means is also connected to the storage tank as well as to the collapsible walled receptacle. The compressor functions intermittently to remove vapors from both units. The collapsible walled unit includes a level sensing means which is adapted to in effect, sense the volume of vapor held within the collapsible walled receptacle and thus to actuate the compressor control means between predetermined levels.