We had a blockage in our kitchen sink once and my mum tried to use Drano. She managed to get it on her hands and copped a nasty skin burn and had to go to the hospital. She also dropped the entire tub on the ground after getting burnt. Then it managed to open a hole in one of our pipes (ancient plastic). Thankfully it was on the outside so was easily patched, and tbf it seems like it didn't actually create a new hole in the pipe, just dissolved something that had been used to seal a small hole in the pipe before. But that was definitely a good learning lesson for me