Q. Can one do an enema on Shabbath?
A. Mishna Berura (328: 55- 56) seems to prohibit. However, some Poskim permit with a shinui or a change from the usual way to do it, when the water used is pure and does not contain any medical substances. The reason being is that it is not a cure but rather only a cleansing of the lower bowel. (Daas Torah (328: 49), Shemiras Shabbos K’ 34: 11. permits even without a shinui. See similar in Piskei Teshuvos 328).
Horav Shlomo Miller’s opinion is that it could be done when needed and only when using only clear water without any medical additives.
Rabbi A, Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a