You can find the location of the leak, but it requires some work. Connect an air compressor hose to the roof black vent. Set compressor regulator to 2 - 5 psi. If you have a sealed system, the black tank will start expanding. You will hear it. Don't worry, it's no where near busting. If the tank does not start expanding, you have an air leak. Start smelling around the toilet. The location will be easy to detect. I had a leak from the cable that activates the water valve. I also had to insert a screw type expansion plug in the bathroom sink.
Sal