2002 Holiday Rambler 2nd rear black tank

When you have 2 Black tanks, they are NOT connected to each other. Each tank has its own dump valve. As the other poster stated, the RED light means the tank toilet sensor(NOT the same sensor as the tank fluid level) is registering the tank is FULL and the toilet will not flush. This sensor prevents the user from overfilling this Black tank because the toilet has its own waste pump that grinds and pumps the debris to the tank. Since you have an odor, that probably means the tank is full and has OLD waste in it. OR, the tank is almost empty and was not properly maintained and flushed and dumped and the build up of debris has tripped the FULL toilet sensor. These sensors for the Toilet are glued to the exterior of the tank and are not into the tank like other probes. There are usually 2 glued on sensors. 1 for half and 1 for full. Doug