Abstract: A pipe tee unit which may be mounted to a pipe for attachment of an extension tube to the pipe. The tee unit is formed of a pair of clamp members which are each formed with a circular concave recess of less than semi-circular section on their respective inner faces for clamping about a cylindrical pipe. One of the clamp members is externally fitted with a threaded nipple formed with a through hole for use in guiding a drill so as to cut a hole in a pipe clamped by the two members, when the two members are bolted together about a pipe. An extension tube fitted to a threaded collar is then fastened by the said collar to the nipple.