The water is veeeeeeeeeeeeeeeeery slow to drain from the bathroom sink. Kitchen sink and shower ok. Have taken it apart at the sink end all seems well, got underneath to where the pipe enters the waste tank but can't get to as chassis in the way. The only way to disconnect is drop the tank and that's not happening. I can't see any fault with the pipe so wondering what will clear it other than a plunger (a bit heavy handed, did this before and it cost me a new sink ).