I have 2 x 50 ltr air compressors joined together and work well, However I have decided to have a full output.I decided to remove the inspection plug in the end of one compressor receiver and fit a Reducer to half inch and then a on/off valve so when I want full output with Full volume of air I can. Now this morning went along to a Gas fitting counter handed the Guy the plug out of the receiver and said I want a reducer in place of this Bung to 1/2 inch ,He came back and said Well your bung is not 3/4 and I don't know what the thread is either. My question …. Would any one out there now the correct Size and thread of the Bung .. ps Both air receiver/compressors are 50 litre from sealey.