It is a hand held device used to get water from the bucket, a tub, or a bigger tank to poor it on oneself. It could look like a bug mug or a pan, maybe without a handle.
Oh yes, like the Big Dipper and Little Dipper in the sky. Dippers have also been used to drink or draw up water from a well or other low source. For other reasons than washing.
Another word is ladle, but that's usually cooking, like to serve out soup. Most places in Europe have enough clean hot running water that people shower, or climb into the tub and wash there.