I use liquid tank treatments, sometimes. But never the plastic packets of powdered treatments.
I also add Dawn dishwashing liquid to help break down solids.
And just before I get ready to dump the black tank I take advantage of having a wet bath to spray HOT water from the shower head into the toilet and then into the black tank, to help further break down solids as well as providing a greater liquid-to-solid ratio so the macerator pump doesn't have to work as hard.
I thought getting old would take longer!