i let my used tanks soak overnight filled with water and a medium size bottle of vinegar. it helps to break down the crusty build up and cuts down on the elbow grease.
I will try soaking it overnight with water and vinegar, and then clean it with a scraper and mabey polish it off with a rag. Will avoid toilet bowl cleaner if possible...(might use it if this doesnt work...but only as a last resort)
i use razor blades for water stains and use a power washer and vingar on em.
Oh and whats a power washer (i blane the fact that were from diff countries to why i don't know....but im picturing a mini floor buffer....)