883. When to End a Personal Fast

127:6 On a private fast, one may rinse his mouth with water in the morning.

127:7 If one accepted upon himself to fast without any conditions, then he must do so until three stars come out at night, even on a Friday night. (The Rema says that he only fasts until he has left shul on Friday night, by which point he has accepted Shabbos – Mishnah Brurah 249:21.)