It's actually a strong acid which is used to dissolve all kinds of stuff stucked inside the pipe, like hair, cloth, tissues and whatever normally water insoluble stuff.
Today I used one bottle again, and I found the U-tube was very hot. This bottle seems stronger than the others, for the smell, and the sound was both stronger. And on the bottle, it shows that it's the enhanced version, no wonder why. The U-tube was so hot to touch even with a glove. I was a kind of worrying.
After I guess around five minutes, I went inside the kitchen and checked again... what a mess! The U-tube cap was on the floor... obviously, it was heated by too much that it expanded and thus got loose from the upper threaded pipe! I used two layers of gloves and a lot of newspaper to suck up the mess... and then I used a lot of water to clean the floor... the floor was very clean afterward, you know, those were very strong solvent, able to clean virtually all kinds of dirty stuff and stain!
Just be extremely careful when you use this kind of strong acid, everything can happen!