What does everyone use to clean the soot off the transom?

Hull cleaner. Then wax and more wax so it is easier next time.

I have always used Atwood hull cleaner and put a spray nozzle on the bottle. I little goes a long way

Vinegar on the tips and soapy water on the transom. A light coat of wax on the transom after every washing. The vinegar works good on the drive too.