Factory-made boots are the simplest and most reliable means for sealing a penetration.
This site-made metal flashing is less reliable than a factory-built one.
Factory boots for these vent pipes are reliable and easy to install.
A factory EPDM collar for this plumbing vent is more reliable than a site-made flashing.
Rectangular penetrations are flashed using skylight details, with overlapping layers of flexible flashing tape.