They're black rubber couplings, available at any Home Depot or Lowe's, in the plumbing department. They are maybe 4" long with a hose clamp at each end. The PVC pipe fits inside the black rubber coupling and you tighten the clamps. They're commonly called "FERNCO Couplings." Their primary application is to make repairs to existing vent and drain lines in your home. They're available in all different sizes, so be sure to get the correct size so that the pipe will fit inside - they're about $3.50 apiece in the 1 1/2" size. Measure the outside diameter of the pipe, and the inside diameter of the coupling, and be sure they're the same. One thing to note: the hose clamps that are included with them don't have stainless steel screws - the screws are galvanized steel and will eventually rust. So it'd be a good idea to replace them with clamps that do have stainless steel screws.