Some copper vessel sinks are design the way a part of it is dropped in to bathroom counter and the remaining, the apron is outside of it. Bath sinks such as this that are called sometimes double wall are more expensive that the regular designs. The reason? There is twice as much hammered copper needed to make it. A copper vessel sink for bathroom have the same drain size as a regular wash basin. It is 1 1/2 inch diameter and any standard plumbing hardware can be used to connect it. The fixture must be without a drain back capability.