We do not use any harsh chemicals. Only use Calgon, liquid detergent and a little bleach mixed with water. We use 2 ply tissue and it all goes down into the tank. Also we use lots of water when flushing. Don't empty the black tank every day. Wait until it gets more in there.
Have not had a problem with all 4 fifth wheels we have owned.
We use the store brand liquid detergent, laundry or liquid dish soap.
Also we use the store brand 2 ply tissue. There are some heavy tissues that we don't buy for the trailer. Such as Cottonelle.