GE Triton Dishwasher Does not drain out completely

My GE Triton Power II diswasher is not draining out water completely. I have cleaned all the clogs etc. Looks like piston and nut is broken. I opened 4 screwes in the rear but not sure how to take out Piston and Nut so that i can replace this with new one.

pls advice.

Just unscrew it (CCW).

Gene.