What is Wash up?
Wash up is (verb) 1. to clean objects such as dirty cups, plates, knives and forks with water It took us hours to wash up after the party. My brother’s washing up, while I’m sitting watching the TV. 2. (of the sea) to bring something up onto the beach It’s interesting to walk along the shore to see what has been washed up onto the beach during the night. 3. US to wash your face and hands He went into the bathroom to wash up.
source: Easier English, Student Dictionary Upper Intermediate Level