I know this is an old post but I would like to explain how I got Nikolai to use the potty bell. We started training this at 8wks old.
First I got a a sleigh bell and tied a 8in string on it and also the door knob.
Next every time we went out to go potty I would have Nikolai sit in front of the bell and I would pick up his paw and hit the bell and attach the leash.
We only hit the bell for potty. If we go out for play or a walk we don't hit it and I use a different leash.
A few times he hit it thinking he could just get outside to play but we got straight to the potty place and wait to go. Now if he can get it he will bring me his play/walk leash.
Now he just goes up to the bell hits it once or twice and sits and waits till I come put his leash on to go out potty.