I never used the procedure once until once on the way home the temp shot up and the system emptied itself.
To fill remove header tank cap, stat blank cap and rad blank cap, fill header tank to correct level until it remains steady, refit header tank cap,fill up stat hole till rad hole is steady,refit rad bung, then fill up stat hole until level steady, refit stat bung, do not remove header tank cap with the bungs removed, done it like this and never had any probs.
If plastic caps knackered go to plumbing place and get some 1/2" bsp rad bungs these are a pefect fit and some come with an integral o-ring, cost about £1.00 each.
Lynall