Gray Water slow flow solved
I finally got the old girl out for another trip and selected a site with 3 way hook ups. I started with a lot of water down the vent stack. The wife monitored the flow via a clear piece and reported several black clumps of something passing. Moved hose up and down vent stack for quite a while. Flow was clear. Loaded gray tank and checked flow. Didn't seem fast enough so stuck hose into valve and then worked it into the gray tank and gave it a good flush. Finally loaded gray tank including hot water and dish washing soap. Then let it go and flowed really well.
Thanks for the good advice, problem solved!