Abstract: A plumbing cleanout fitting combination, of a body having a plug-closed access opening provided with a female standard tapered pipe thread, and a somewhat counter-bore-like seal seat around the outer margin of the opening; an elastomeric compressible gasket or seal ring in the seat; and a plug having a shoulder at its outer end to sealingly compress the ring and, on its inner end, an opening-engaging male thread, of pitch corresponding to the female thread, the male being either a standard straight or modified tapered pipe thread, diametrically proportioned to the female to enable the plug to be screwed in to seal without thread interference; whereby the body can accept an optional plug with a male standard tapered pipe thread sealing by tapered thread engagement without sealing gasket.