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Mike that is a filter/drain to remove water out of the air system. Is it in the engine compartment? Or the generator compartment? There are 2 black plastic pieces that you slide down then rotate the bottom (probably counter clockwise) and pull it down. I think it is a bayonet mount. The o-ring where the bottom attaches is known to leak, also the glass or plastic can develop cracks over time. They are readily available on Amazon, ebay, Graingers, etc. There should be a valve at the bottom to drain the water collected, that could leak also. Another thing is the push-on fitting with blue air line are leakers also. Can you run the engine so that the pressure is at normal? Then you could spray everything, that filter, all fittings, even the hoses can develop splits and cracks. Any soapy solution works well from soap/water to windex. All you're looking for is the bubbles to become apparent with air leaks.