Spray evenly and carefully. Spray it with the hood up. Allow to air dry. Spraying a garment manually is an inexact art. You don't want it to leak anywhere, so repeating the procedure increases the likelihood of thoroughly coating the whole thing.
Air dry again.
This whole process, admittedly, sounds like a pain in the ass. Actually, it was. For me, it meant busing out to my folks' place and tiptoeing through the cat poop in the basement laundry room. Breathability returns within a few wearings. Another option, of course, is the Hefty garbage bag.