What has me concerned about what the OP said, hopefully I read it wrong, after dumping he disconnects the sewer hose and continues to flush for an hour. Where does the water go. At first I thought he was rinsing the were hose with a water hose but the said he does his tank. This stuff cannot go on the ground. I also cringe when I see people stick a hose into the sewer hose, now that hose I'd gross and unusable for anything.
I have never timed it but I dump the black, go inside an stand on the peddle for a couple minutes and then totally fill the bowl 2-3 times to flush a rush of water. Go outside an close the black nod open the gray. While that is happening I go in, add water to the black tank and add the aqua chem. go out, close the gray, put the sewer hose away and wash up. This is all done at the site as we only go to full hookup sites, have never used a dump station.