Reversing pump maybe doesnt reverse

Can the reversing pump on a single-pump model fail to go in to the drain cycle, yet work in wash and rinse cycle? I have had it all apart 3 times. Here is the diagram. http://bot.searspartsdirect.com/partsdirect/part-model/GE-Parts/Dishwasher-Parts/Model-GSD2100N10BB/0432/0130000/G0901051/00003?blt=06&prst=&shdMod= I thought maybe I was putting the white plastic check ball in the wrong place, but I’m dropping it in the tube from below the fine filter. This diagram does not show that there is a rubber flapper in the pump itself, at the port from the hose shaped like this: . And I even think I felt a rubber diaphragm not shown in the diagram, in the collection chamber, on the wash side(I think). Does anyone know? Maybe that isn’t supposed to be there. Maybe it is a renegade piece of trash that needs removed. Has anyone workrd on this model before, or one similar, if you look at the above linked diagram? Please give me any advice. I have checked everything I can see in the diagram, but like I said, some things aren’t in the diagram.Thanks. Oh, and the solenoid works on all cycles, as timer asks it to, and the rubber flapper did close right when in my hands, manually pressing the solenoid.