I am trying to replace the pop-up drain in my bathroom and have gotten the old pivot rod, seat (or flange), and stopper removed, but am having trouble figuring out how to get the drain body and drain tube out because the gasket prevents you from lifting it out through the sink (and i do not see a way to remove the gasket). Do you have to remove the trap? The directions on the replacement unit I bought do not address this. Thank you!