I have discovered a large pipe under the holding tank access door that has four nested straight green pvc pipes that appear to be for connecting the drains. The problem is they are straight thin wall with no connectors and the ends are just flush. Did Barth make some sort of hose support system (1993 Regency) that the typical accordion hose we all know fits into?
Thanks
Tom

Hawk, those sound very much like the hot water, freshwater, and fresh tank over flow drains.

They are not used except at season's end.

They should go to a series of valves, and are used to drain your water system for winterizing.

Your post was not clear, but did you think they drained the black/grey tank?