Waste-plugs are generally of brass, carefully ground to fit the washer, but the weight of a large plug of this kind is so great as to damage the enamel of the sink if the plug is allowed to fall upon it from some height. A slight improvement is effected by covering the plug with indiarubber, as shown in fig. 36. Plugs of solid indiarubber are better in this respect, but are apt to get out of shape, and are now giving place to vulcanite, which is light, clean, and durable, and therefore well adapted for the purpose. Sunk brass plugs have, however, the advantage of not forming any projection above the bottom of the sink.

The size of the waste-plug and grate will depend to some extent upon the capacity of the sink, but the larger they are the quicker will the water escape, and the better will be the scour through the trap and waste-pipe. As a rule, the waste-pipes of sinks should not be less than 1 1/4 in. in diameter, and need not be more than 2 in. It is a good plan to have the plug and washer at least 1/4 in. more in diameter than the trap and waste-pipe, as the trap is thus more easily kept clean. This can be done by means of the tapering washers and tails illustrated in figs. 30 and 32, or by using a washer and tail of larger size than the trap, and belling out the inlet of the trap as required.