In my house we are accustomed that when somebody needs to do gedolim, he spreads out a bag over the toilet and defecates in it to avoid clogging up the toilet with the excrement. Then the bag is discarded in the garbage.
May one do this on Shabbos, as excrement is muktzah, and one is being mevatel a keli, plus one cannot carry (the bag outside) on Shabbos? What would the rav suggest we do for Shabbos?
It isn’t a problem of bitul kli m’hechano, because a plastic bag is often used for garbage. Regarding taking it out of the room, (or house if there is an eruv) on shabbos it is permitted because a kraf shel rei, i.e. a disgusting item although it is muktza, it may be removed.
Kovetz Lev Yam Shabbos pg.89 in the name of R’ Eliyashiv and R’ Neuwirth zt”l, O:CH 308-34.