I flush mine at the dump station by filling it once after initial dumping. Before I leave a dump station I put about 5 gal of water in the black tank, no chemicals. Once I get home I dump it in a bucket and pour it around in the grass or flowers. I have dogs, cats, deer, squirrel and birds in my yard doing the very same thing without a bucket. I also pull the grey tanks valves open let them dry out for a day then close them back up.
No man has a good enough memory to be a successful liar. Abraham Lincoln
2016 36FBTS Pinnacle
2016 F350, 6.7, 4x4, DRW, long bed
B & W Companion 5th wheel Hitch