Unless you enjoy watching the plumber hanging out under your sink or love the scent of drain cleaner, you must make sure you never let these two things enter your pipes. Grease and potato peels are apparently the worst things for your plumbing system, which can create backups and blockages. Thanksgiving tends to be the time of year where most of us allow it to happen. So much so that plumbers have termed the day after, "Brown Friday". According to Doyle James, president of Mr. Rooter Plumbing, grease solidifies in the pipe and becomes difficult to remove, while the potato peels jam up garbage disposals.