Drano has caustic chemicals in it. It may hurt the tank, seals. Don't think it it safe for septic systems which a lot of parks are on.
There are plenty of RV safe chemicals out there you can use.
Not sure why ppl are so concerned about having a squeaky clean black tank. It's just going to get dirty again when you use it.
Make sure you have a few gallons of water in it all the time.
I like to dump when I first get to the rv park. That way everything hasn't settled yet.
I am no expert but this has worked for me for years.
good luck