Ended up buying a camco sewer flange to 3 inch npt adaptor online. HD I got a 1 1/2 cleanout fitting glued that into an adaptor/reducer to bring it up to a slip fit/female threaded pvd 3 inch fitting. Nice neat setup on the input side to the pump.
Output a clear 1" hose to a 3/4 nipple/3/4 tee/ another 3/4 nipple and a 3/4 npt to male hose fitting. Off the tee I attached a hose shut off valve so I could hook up a hose to wash out the discharge hose.
Tried the gray tank first. No problem.
Black tank: Pump handled the discharge into the 5/8 hose but would heat up and shut down after about 3 minutes. I gave it a rest to cool and repeated. Worked well.
I have two 5/8 hoses so I was thinking I could always use the tee fitting and hook up another hose to use as output. But as it is it did the job. I think I might have had trouble if it had to go uphill, but since I was level it worked.
I attached a water hose to the tee and flushed out the discharge hose and put that back into action for the garden