Who is the Regulating Government Body that oversees Washbays?

This depends on what State you are located in, but generally it is the Government body that looks after the sewerage/waste water and water supply in your area.

For example in the Sydney region this is Sydney Water, in Western Australia this is the Water Corporation and in Lithgow NSW it is the City Of Greater Lithgow Council. Other Environmental Bodies and Catchment Management Authorities may also be involved.