washbowl
A small round or rectangular bowl, used for washing the body during bathing, or for washing dishes, small articles of clothing, etc. Most commonly seen during sit down bathing in bathrooms, or as small wooden buckets in onsens. Also known as a washbasin.
The Naigai Yakuhin Company is known for distributing washbowls to public onsen across Japan to promote their Kerorin brand of aspirin.