I've always just put them through the wash on warm/gentle cycle but the other day my gf asked me "so will these things ever leave any junk behind in the washing machine"? Being the good deflector that I am I told her "nah, nothing to worry about" but it got me to thinking... as far as things like wax go, have you ever found traces of it on the next load of laundry you ran *after* you put your MFs through? I think my gf would absolutely flip if a load of clothes was ruined by residual junk from my MFs.