Devin, welcome to the asylum. We are here to answer your questions, and occasionally the answers we give will be correct.

You may not have realized it, but you have a leak. (Just kidding, you apparently know you have a leak.)

Ignore the toilet for a moment because that does not appear to be the problem. It sounds like the leak is so large I suspect you should be able to hear it. Just to be certain your bus is roadworthy, and the leak is in the aux system do a DOT brake check. Turn the engine off. You should be able to engage your service brakes, and except for the small pressure used for the brake application, the two air systems should not drop. If that checks OK, chock the wheels and relase the emergency brake. Again you should see a small pressure drop and then the gauges should show no further loss of pressure. Everybody should be doing this brake check prior to any travel. The final check is to fan the service brakes, and at some lower pressure, 60 or 70 pounds you should hear the audible alarm and the warning light should come on. At 40 to 50 pounds the emergency brake knob should pop back up.

Now we return to the main problem, assuming the brake system checks OK.

Bring up the air pressure by running the bus and as soon as it is at max pressure, turn off the engine and listen. With a leak so big the aux compressor will not keep up you should hear the leak. If you cannot hear the leak your job just got much harder, but there will be no shortcut. The leak must be found.

Just for your own information, I believe your bus has a suspension system that requires you to maintain aux air pressure of at least 35 PSI at all times or the valves back above and between the tag and drive axles will dump air from the rear air bags.

There are so many potential points for leaks nobody here can point you at any specific likely starting point. Once you can pinpoint the leak area, even if you cannot see it, let us know. We can probably help with fuirther info.