Lather, rinse, repeat
Rinse and repeat; Wash-rinse-repeat; Lather-rinse-repeat; Shampoo algorithm; Wash, rinse, repeat; Rinse repeat
Lather, rinse, repeat (sometimes wash, rinse, repeat) is an idiom roughly quoting the instructions found on many brands of shampoo. It is also used as a humorous way of pointing out that such instructions, if taken literally, would result in an endless loop of repeating the same steps, at least until one runs out of shampoo.