Is it obligatory to wash the base of the Western toilet before and after use if there is doubt about water impurity on it, and does this doubt necessitate treating everything in the bathroom as potentially impure, especially since I had overcome obsessive doubts regarding purity?

"Leave aside the obsessive thoughts about washing the private parts. You are not required to wash them before or after relieving yourself unless you are absolutely certain, with definitive certainty, that they have been soiled with impurity. The best cure for obsessive thoughts is to ignore them and pay no attention to them. Continue to strive against them and disregard them. The default state of things is purity, and this principle should be applied if preventing the mere suspicion of impurity leads to obsessive doubts."