Has anyone used this to purge their Hot Tub? We bought a used tub yesterday and stopped by the Hot Spring Store and I told them I wanted something to clean the pipes and he grabbed a canister of Clean Start. He said only use 1/2 of the canister since we have a smaller tub. It is supposed to clean the pipes of mold and junk. Then it has to sit in the tub for 12-14 hours. Just wondering if anyone has tried it and how it works.