Abstract: A roof flashing for establishing a weather-proof seal with upstanding pipes of different diameters includes a frusto-conical shape collar having smaller diameter upper and larger diameter lower seals for sealingly engaging different diameter pipes and an internal annular groove immediately above the lower seal providing a frangible wall section in the collar to facilitate removal of the upper seal from the collar when the collar is to be used to seal against larger diameter pipes. Immediately below the internal groove on the exterior wall of the collar is an external annular bead which together with the lower seal resist stretching of the collar when engaged by a gripping tool immediately above the internal groove and pulled to provide a relatively clean tear in the region of the internal groove around the entire periphery of the collar to separate the upper seal from the collar.