Good question! We worked out a central location for the drain and supply lines in the middle of the island. After the island was in place, the installer made a small box around them out of toe-kick material provided by the cabinet company. This box is practically invisible from most viewpoints unless you really look under the island.

Another trick is that one of the legs is hollow and that is how we ran the electrical. There are outlets on the side of the island facing the main sink.