Draining gray and black tanks

Thanks for the tip Mitch.  I will share that info with my newbie husband.
I have watched many video anout cleaning the black tank and I doubt ours is as clean as I would desire.  We use the chems recommended, but we didn't use the ice cubes and had nowhere to dump after draining and popping in the chems.
New tips appreciated.
BTW, fellow forum members, our 12 day trip had sewer at the site and Mike did a good job.  He was cautious that connections were solid, I had a nice little sewer kit with gloves, Clorox wipes, hand gel and Clorox spray for any possible clean ups.