Eriez's reversible liquid vacuum is a good solution for the pump cleaning problems. It may be compact in size but it can quickly suck tramp oils and waste coolants without any hassle. The air control valve is included in its feature.
With just a turn of a knob, the vacuum will release liquids out of the drum into a different container. This can be operated on shop air. Moreover, it links to a small bung on a standard drum as it contains a single maneuvering part.
Unlike the other vacuums, it has a whisper silent exhaust. Meanwhile, it does not need further maintenance.