Does rinsing the mouth invalidate the fast of a fasting person, whether the fast is obligatory or supererogatory?

The fast is invalidated, according to the Malikis and Hanafis, if water reaches the throat during rinsing, absolutely. As for the Hanbalis, the fast is not invalidated if that was due to rinsing during ablution. If the rinsing was for other than ablution, then if it was for a valid reason, it does not break the fast. But if it was in vain, there is a difference of opinion regarding its invalidating the fast.