If water gets inside the anus when doing instinja’ (cleaning oneself after defecating), that does not break the fast, because this is not food or drink, and it does not come under the same ruling as eating and drinking. We have already explained in the answer to questions nos. 22959 and 22927 that enemas and suppositories which are placed in the anus are not things that break the fast.
We advise the questioner not to burden himself with such issues, because there is no need to make water enter the anus on the grounds that this is more cleansing. This is a kind of going to extremes in religion, and the Prophet (peace and blessings of Allaah be upon him) said, “Those who go to extremes are doomed.”
And Allaah knows best.