A hydraulic system for a multiple friction transmission, comprising: a first pressure relief valve 5 regulable by means of a first pilot pressure; a normally-open drain valve 8, which is a directional valve switchable between an open state and a closed state by means of a second pilot pressure; at least one first pressure regulator 11 for operating the drain valve by means of a first pilot pressure and a second pilot pressure, respectively; wherein in the event of detrimental hydraulic pressure build up, the second pilot pressure is dropped to open the drain valve, so as to relieve pressure through the drain line.