Abstract: A method of trimming plastic covering a mouth opening of a blow-molded universal urinal involves rigidly holding the urinal in position opposite a trimming machine. The machine mechanically moves a knife mounted thereon in an oval pattern in one plane while simultaneously moving the knife in an alternately concave and convex pattern in a second plane orthogonal to the first plane. The knife is mounted on a platform which is movable in the second plane independently of the movement of the knife. As the platform is moved toward the urinal mouth, the knife is moved in the described pattern, thus smoothly trimming the urinal mouth.