How do i install plumbing vent flashing?

I need to replace my some plumbing vent flashing. I have an Oatey No-Caulk (plastic) vent flashing. I've been reading (and watching) various web sites and they say nothing about sealant. So I am to nail the flashing down without putting any sealant on it? I know to put sealant on the nail heads and underneath some of the shingles, but nothing on the flashing itself? Thanks, JT