DTW Storm collar (required only if roof flashing does not seal to pipe - Stovefitter's Warehouse
Goof Proof Shower Goof Proof Waterproofing Sheet Membrane Underlayment Flexible Pipe Collar 4.25 in. x 4.25 in. x 20mil GPFPC-Flexible Pipe Collar - The Home Depot
Underlay sealing collars - Klöber
Application issues and pipe penetration seals - Promat