Stinky Question

Put a pint of pine sol in the black tank. Then see if you smell Pine sol outside. If NOT, then repeat with the Gray tank. This will determine if you have a tank leak or venting problem. usually, if you flush the Black tank and DO use chemical in the tank, you should NOT get any Black tank odor, just the smell of the chemical. GRAY tank odors are far worse than Black tank odors and most people do not think of the Gray tank causing the odor. If you can open the toilet valve with no water on and you do NOT get a foul odor, then the Gray tank is suspect. Also, a Washer/Dryer ABS drain line that the water has siphoned out of the P trap will cause Gray tank odors also. Doug

BTW, The Cyclone type vents people install just HIDE a problem. If you have to use those to get rid of odor, you need to find and fix the cause of the odor.