[RichardJ]

I usually get some rubber hoses that fit tightly on the inlet and outlet of the evap. With both hoses held above the evap, I pour the flush in and let it soak for awhile. After the soak, I lower the outlet hose into something to collect the flush. It isn't all going to come out on its own. You will have to blow it out so the collection container needs to be something that can accept the flush and a big burst of air without spraying that crap all over everything and yourself.
If the flush comes out dirty, you will need a second flush. Then it's a matter of blowing air in from alternating directions until you think it is all out and dry..