Hydrochloric acid. It's the very best, and you only need a cup full. Not now sold to the great unwashed, but just get a tradesman to get you some.
Hardware stores stock the gentler version, called Spirit of Salts, but you might need two bottles (about £3.00 each when a bought it a few months ago).
Both are very nasty to use, stink to high heaven, but get the job done once and for all.
Briefing against women ministers in Westminster
Walking sticks in "tottery" in old age
What’s a household item that reminds you of your grandma’s house?
