I believe it's Pink Stain Remover
The pink powder that HBS's sell (which is overpriced imo)
I use hot water to rinse (or a scrub with some bi-carb and a cloth if there is build up) then a soak in Starsan
The Starsan should eat most things off the surface of the glass, then a rinse in hot water again leaves them spotless
It's Chlorinated Trisodium Phosphate and works well on glass, I use it to clean all of my yeast jars and flasks and also to clean and sanitise my bottles before bottling. Haven't tried it for the drinking glasses but no reason not to.