Grey tank can smell as bad as black. We add chemicals to our grey tank also. Bad valves under sinks can cause odors from grey tank to come into the RV. If you have a washer dryer that you haven't used in awhile, add some water. The trap dries out.
Also check the batteries. Batteries without water have a terrible smell!
In the summer when temperatures are high, we have to add 2x as much chemicals to the black tank.
Has anyone full timing used the new Dometic chemicals for full timers?? Saw it at Camping World.