Draino is a complete waste of money. I buy the stuff called Instant Power Hair Clog Remover. I found it at Walmart, it's roughly the same price as draino, it's safe for all pipes, and it works. I've used it several times. I'm female with long hair.

One time, many moons ago, I went to the hardware and asked them what to get and the old guy handed me a bottle like a giant pill bottle with dry gray chips in it. I wish I could remember what it was. All I know is that it cost twice as much as Draino and was fun to watch. You pour the chips down the drain and stand back. It emits a gray smoke as it eats away all the crud in there. My sister was living with me at the time, so twice as much long hair clogging it up. I'm pretty sure those pipes were cleaner than they were when they were installed. I wouldn't use it on PVC pipes though.