Your signature does not list what type of trailer/RV you have... there is one other place that the odor you are describing can emanate from. If you have a rig with a outdoor kitchen, two baths or with a half bath that are on opposite ends of the coach, many times there is a air emitter installed in lieu of a vent to the roof (air emitter is a one way valve that allows air to enter the drain line- this is done to stop the traps from being siphoned dry) There is a very lightweight internal rubber flapper that allows air to enter when needed. These units tend to fail and allow tank odor to escape.
Take a look around for something that looks like this:
Sometimes behind a access panel, or in the back of a cabinet, or behind a set of drawers.
See if your odor is concentrated around it.
Easily replaced and available at most big box stores for about $10.
2014 Rockwood Ultralight 8312SS Diamond Edition
2011 F150 Super Crew 4x4 5.0L - Traded!
2016 F350 Lariat Ultimate Super Duty Crew Cab 4X4
Northern NJ - God Bless America!