Well, I know a lot more now than I knew before. The carpenter took off the Sheetrock in our storeroom behind the bathroom that was smelling. Little or no trace of mice.
So we went around the whole foundation and outside of house. We have two vents outside coming through our brick. One of them is a dryer and the other is a vent from a basement bathroom exhaust fan. Dryer vent checked out ok, but the other vent had a few mouse turds in in, soooooooo we theorize the mice walked up the side of the brick and made their way in through there and that is why we are guessing there is a strong odor in the bathroom. But we believe they chewed through the flexible vent hose and got out into the basement.
The vent has been replaced with a new one with added metal screen on it. The question remains no mice can get in now so we just have to trap any remaining mice now. We haven't caught any in five days now in traps, rodent motels, sticky baits or rat zapper death by electrocution.
The ceilings in the basement are all sheet rocked and finished so I can't get at the vent hose.
My options are to 1) continue to trap to catch any remaining mice that may still be alive; 2) have somebody with a flexible seeing eye gadget look into the vent hose/tubing to see if they can see anything or any problems in the hose or blindly take out Sheetrock in the ceiling of a bedroom adjacent to the bathroom and the bathroom and replace the vent hose.
Comments are welcome.