That indeed was the basin for a commercial D2, while very uncommon to find we do have one at our office that we have used to clean my distributors rental property with a D2 brown power nozzle. If I get a chance I will snap a photo of it for ya.
There was no 'commercial' motor unit, only the optional 2 gallon and 5 gallon pan, along with a 15 inch wide bare floor tool, and a 15 foot long hose. Everything else was household style.