I do not have photo's at the moment.
But if you remove chemical bottle 1 at the front side, you should see the drain opening on the tempering bath.
The stop in the drain is some kind of rubber stop connected to a spring that is pressed down into the drain, and connected on the other side to the handle that you can reach on the side of the chemical disposure.
If the rubber stop and spring is missing, you could replace that with a "normal" stop and keep the water in the processor all time.
You should not make a valve in the chemical drain bassin, it will eventually overflow and all chemicals will polute your tempering bath.
You can put bottles in the chemical drain bassin to collect wasted chemicals, so that stop and fix can be reused.