The technique of washing your arse after having a shit and not having any other way to clean your arse. the double flush is done by flushing the toilet, cupping your hand and cleaning your arse with the flush water.
Maj: Theres no toilet paper and I need a shit.
Kamy: Just do the double flush, intit.
Zed: Whats this double flush business?...Im hungry.
Kamy: You know, double flush it, intit. Put your hand under the water and clean it! Intit!