I have a slow draining tub that left me standing in water at the end of a shower. This happens about once a year. I found on-line to try Nair, Dawn detergent and boiling water. It helped somewhat but still a problem. Then I poured an entire package of Cascade down the drain and flushed it. Voila!
It clearned out the hair and soap clog and it works perfectly and has kept on doing so. The plumber charged me about $175 every time to clear this drain.