To prevent the rusting of a compressor air tank and thus smoothly discharge drain water by bending a silencer pipe projected into the air tank to direct the discharge from the tip discharge port thereof substantially horizontally as well as away from the wall surface of the air tank near the arranged position thereof.

A silencer pipe 5 is bent to have an angle which permits its easy insertion through the hole of a socket 1a welded to an air tank 1 and causes no excessive restriction as to affect its silencer effect or discharge resistance. The discharge port of the bent silencer pipe 5 is directed horizontally away from the wall surface of the air tank to the utmost, because the discharge from near the wall surface of a mirror part thereto is more liable to produce pinholes due to rusting and noises like in the case of the discharge from a straight pipe to the bottom of the air tank. The horizontal discharge causes no agitation in the liquid surface in the vicinity of the suction opening of a drain pipe 2 for sucking drain water up, to permit the complete discharge of drain water.