oh could you explain a little more?
the chainsaw bit has been updated to have a new puzzle so videos of that part might be a bit outdated! now when you enter the room you got the chainsaw, youll notice theres a few pillars with lights on them, interact with them and the room will change when you solve the puzzle and a new path will open on the bottom left side of the room!
you dont keep the chainsaw when you enter the sewer though, you no longer need it down there O: theres a water box puzzle youll need to solve to progress in the sewer, lemme know if you need help with it!