Abstract: A flexible valve that includes a flexible sleeve inserted in a fluid line and made with two circumferential folds, two opposite slides located between the folds displaceably in phase opposition and extending crosswise of the sleeve, and a mechanism for displacing the slides between open an closed positions. A sleeve section connects the two folds, and a closing section made on the sleeve section is supported by the slides. The flexible valve according to the invention has a longer service life and a shorter installation length than hitherto known. It is suitable for use as stop valve in the drain line from a toilet in a railway carriage, in which it can be continuously kept in the closed position without applying energy, and it is furthermore safeguarded against impurities getting out into and fouling the surrounding environment in the railway carriage.