The connection of the soil-pipe with the closet-pan is its weakest point, and the most liable to leak. The main difficulty consists in forming =joints between earthenware and metal=. Socketed connections are not safe. The use of an india-rubber ring inserted between the lead and earthenware flanges and bolted together by means of a brass collar and hooked bolts makes a fairly good connection. Various screwed connections are made. In another form the earthenware collar is covered outside with lead, so that a soldered joint can be made between the earthenware trap and the soil-pipe. In the “metallo-keramic joint” the earthenware joint is painted over with a metallic solution and fired. To the metal film thus formed, lead or other metal can be firmly soldered. The connection of the soil-pipe into the socket of the first pipe of the earthenware drain requires also to be carefully made. This pipe is curved, and at its upper end has a socket, into which the soil-pipe enters. A length of brass or copper tubing known as a “thimble” (about a foot long) should be soldered to the bottom of the soil-pipe; the rim of this thimble rests in the socket of the drain-pipe and the space between the two is filled with Portland cement (Fig. 30A). With the ordinary connection between lead soil-pipe and drain, the former is apt to become dented by blows, and the latter is very liable to be partially blocked by the dropping of cement inside the pipe when making the joint. =The House Drain= under ordinary circumstances receives waste water from sinks and baths, rain-water, and the discharge from the closets. [Illustration: FIG. 31. SHOWING DEPTH OF FLUID AND CONSEQUENT FLUSHING FORCE OF THREE DRAINS CONTAINING AN EQUAL QUANTITY OF SEWAGE.]