by a coiled spring clamp 64 the spring clamp 64 includes finger grips 66 which are squeezed together by finger pressure to release the clamp in a known manner the sight tube 61 visually displays the level of liquid collected in the tank chamber 18 because such liquid passes through the lower nipple 49 seeking its own level in the tube the upper nipple 53 allows air pressure above the liquid to be equalized between the tank chamber 18 and the tube 61 by simply viewing the liquid level displayed in the sight tube 61 a user knows when a sufficient or a certain volume of liquid has been collected in the tank 11 so that vacuum operation can be discontinued and the tank can be emptied in accordance with the invention the tank 11 can be conveniently emptied of collected liquid by using the tube 61 as a drain conduit this is accomplished by simply disconnecting the tube 61 at its upper end 62 from its associated nipple 53 straightening it in a swinging motion and lowering it to or below the level of the tank bottom wall 16 to allow gravity flow of the liquid there is no need to pick up the cleaner unit.