I’m listening it for parts or not working, I have not used it to fill or empty a bulk milk tank. I do not know how well it would seal. It is not new and show signs of use and age. It needs some cleaning. Please use the pictures to help determine the condition of this item. The locking nut take some effort to turn on because it appears that the valve perhaps was dropped a number of times but it does turn on and off. The question mark in the title indicates that I’m not sure of the exact size but I would say the inside diameter is approximately 1 and 3/8 of an inch. The male threads have an outside diameter of approximately and 7/8 of an inch and the inside diameter of the nut that would turn on to the bulk tank is approximately 1 and 3/4 of an inch.