Purus knife is used for making holes in the vinyl flooring, waterproofing membrane and gasket (or sleeve). With Purus knife you get an easily and quickly precise hole measurements for the clamping ring.
That is depening on what floor type the gully is installed in. For vinyl flooring we have round stainless steel gratings and for tile flooring we have square design gratings. The majority of Purus gullies are delivered with a grating in either plastic or stainless steel.