Drains should be located on the low points under the tractor near your final drives and also near the center of the tractor.
Make sure all implements are on the ground and pistons retracted as much as possible to maximize the drain.
Depending on how bad the water is, you can add a bunch of cheap "UDT compatible" fluid after the flush, run the machine and all implements, and then drain fluid and add quality KUBOTA Super UDT2 fluid.