Fernco 3"x1-1/2" Reducing Size Donut. It is a flexible PVC donut-shaped ring for the compression sealing of sewer pipe joints and DWV connections such as sockets, hubs, bells, and spigots. Made of corrosion-proof PVC, it is unaffected by acid or alkali and rated for above or below ground applications. No special tools or sealants are required, and it must be sized within 1/8 inch of pipe dimensions to create a compression seal.