Judi,

Yes you can add another compressor to the two you already have, but your problem still exists.

Think about it for a moment. If you add a small compressor dedicated to the toilet, where and how do your hook it to the air lines? If you disconnect the air lines from the rest of the system (where the leaks are) then you are at the mercy of a small compressor. If that compressor quits, what is your back up? Right now you have the aux compressor and the engine driven one. If you leave the current air line connected, and you "tee" into the line with the new compressor, it will run as much as the aux compressor does now.

It would be a lot easier just adding a compresed air tank and a check valve. At least you would get X number of flushes before you had to run the engine or turn on the aux compressor.

For the amount of screwing around adding a compressor it seems the same amount of time can be spent finding the leaks and curing them.

Wouldn't you rather have the coach right than all cobbled up?