A sleeve for forming a channel through a concrete slab is described herein. The sleeve includes a sleeve body with top and bottom ends extending along a longitudinal axis, wherein the top end is wider than the bottom end. The sleeve includes an attachment flange attached to the bottom end that extends laterally outward with respect to the longitudinal axis. The attachment flange may be secured to a concrete form. An alternative sleeve has an attachment mechanism protruding from the first end of the sleeve body for facilitating the attachment of the sleeve body to a concrete form. In some embodiments, the sleeve can also include a removal mechanism disposed at the second end of the sleeve body to facilitate removal of the sleeve body from the concrete slab. Various sleeve configurations are described, some of which are reusable and some of which are one-time use only.