What the heck is a washbasin? Is that a sink? I hear "washbasin" and I think of old Westerns, those times and places without indoor plumbing.
Yeah. I think it's more of a British thing to say, I can't recall hearing it used here in the US. It means a sink for washing your hands and face, like a bathroom sink.
A washbasin can also be a plastic tub placed in the sink to wash dishes when you are keeping kosher. You will have a washbasin for the dairy dishes and one for the meat dishes, etc.
Yes wash basin is also standard English in Australia for where you wash your hands in the bathroom. Nice change from having to remember the US words for things to avoid getting an error in Duolingo.