No, must have all been smooth the ones I've done. The bungs are 12 quid a pair very long taper of very spngy rubber, come with a piece of string which on first pair you buy wraps itself around every tool in your boc, second pair you buy, you bin the string with the packaging.
Winesaver lever type bung also works in 22mm outlets, I've borrowed those from householders successfully..
Did a school header tank ('bout size of swimming pool) with carton of plumbers mate, but pressure was so immense it wouldn't come out again, had to dive in and lever a gap in the side. Was hairy moment, scared of blocking system with escaping plumbers mate.
Well, who wants to wait for a swimming pool to empty before you can move a rad?
I seldome have success with my pipe freezing gear, and tend to go for suspending system instead, which always seems to work for me.
Of course many times you can just cut the pipe live and get a service valve on before householder gets back with cup of tea. Just wipe glasses off and job's a goodun.