Technik Dishwasher no longer fully draining?

Have Technik SE6TIE1GB/17 Dishwasher. It doesnt seem to ever fully drain. Checked the waste pipe and that seems clear. Took the side off and observed two things. One is that near the top of the metering tank it appears to be full of gunk. This is the area that connects to the airhole. The second is that red plunger in the pressure chamber is full of grim. My money is on the red plunger on the pressure chamber but as I really havent got a clue thought would ask before trying to descale it / replace the pressure chamber. Thanks!