Sewer problems are usually caused by several factors. Start with the easy and proceed to the more difficult.
1. Ensure your P traps are functioning and full, including the washer one.
2. Ensure your roof vent is functioning properly. Did the tech drop his screwdriver or other object down the tube accidently? Perhaps lost a bit of plastic that's now wedged in the pipe? I'd remove the cyclone and run a good bit of water down that pipe to make sure it's not plugged in some way. May be a birds nest, hornets nest etc.
3. Clean your black tank well.
4. Don't poop in the rv. Well that one most likely won't work. :)...Dennis