Hi again,
Did a very rough estimate figuring 18x40 rectangular then figuring a kidney is 1/2 the surface area and that works out to be 225 gallons per inch of depth. Pressure testing is a way of pressurizing the lines with air and checking for leaks. For exaample you would blow the water out of the return lines with air, then cap the return jets and pressurize and see how long it takes the pressure to drop. At least that's the way I do it but I'm not a pool guy in the business. Don't know how they would do a main drain though. Dye testing is simply very slowly, in still water, squirting a colored dye around the suspected leak area and seeing where it gets sucked by the leak. Hope you get it resolved today. Keep us posted.
Al