forgetting to flush the toilet
Refers to the act of forgetting to flush the toilet after use. Often used in household or public restroom contexts.
Please be careful not to forget to flush the toilet.
I put up a notice because people often forget to flush.
Compound of 流し (nagashi, 'flushing', the continuative form of 流す) and 忘れ (wasure, 'forgetting', the continuative form of 忘れる).