A couple tips when flushing cooling-system:
After gravity-draining is complete, use a leaf-blower to blow into top of radiator (where the cap usually goes) You will be amazed how much additional fluid comes out the drains.
Also a reminder - Unless your tap-water is unusually pure.... use ONLY distilled water to flush and mix with your antifreeze. Otherwise, the dissolved contaminants will precipitate out of suspension and form a coating inside your cooling-system which cannot be cleaned off. This coating reduces the effencincy of your cooling system (Kubota cooling systems are already weak with brand new shiney clean metal on the inside)