When I need to clean my Black Tank I use RV Digest! Six capfuls then completely fill your Black Tank and let it sit for 24 hours then drain. The enzymes in RV Digest eat up anything that was put in your Black Tank. Cleans all the sensors and is safe for the enviroment. Then I do spot checks after the cleaning, 5 gallons of water 1/4 cup of Dawn dish soap (blue in color) and let that splash around when I leave to go camping and after dumping my black tank and heading home. I never have used Drano and wouldn't think of it. Good Question and Good Luck.