Michael,

The tempering bath must stay full, in the recovery tank there is a "handle" to empty the tempering bath.
The chemical recovery tank must be empty.
What you now have is probably an over fill because you put a stop in the chemical recovery tank drain.
If the tempering bath is having too much water it overflows in the recovery tank, but when there is a stop in the chemical recovery tank it will overflow.
To check the tempering bath stop, you have to remove the top coverplate on the side where all the chemical containers reside.

I have an ATL3 and have dismantled it all to clean and check for proper working.
It is not hard to dismantle the machine, just do not force things.

Mike