Schedule 40 PVC Pipe Fitting SLIP x SLIP Reducer Coupling (4" x 3" (1 Pack)) - 429-422 Slip Reducer Coupling for Schedule 40 PVC Pipe (Slip x Slip). Slip reducing couplings are used when the pipe doesnt need to be taken apart and you are simply joining two pipe ends together. Both pipe ends are glued into the coupling, forming a joint. All of our Schedule 40 fittings are NSF rated 14 & 61, which means they are certified for use with potable (drinking) water. Maximum temperature is 140 degrees F.