I have started a new thread because the other one was getting rather long.

1) We use ordinary water, so that the resin sinks (this would allow the use of heavy fillers which is what I was after).

2) The laser fires through the bottom of the tank (where the resin is)

3) we drip in water from the upper tank using the existing calibration and valve

4) A floating platform (loose interference fit to the tank walls), sitting on the resin rises up on the water and pulls the print upwards

Voila, no O ring and heavy resin fillers possible. One extra part, the floating platform. We know this works amazingly well from seeing the Form1 prints and the peachy team need only make one extra part, the floating platform. Plus you dont have the bother of making brine.