The drain pump on a dishwasher will always be located at the bottom of the machine, some can be accessed from the front as in this video, others you can removed from under the base of the dishwasher, But the first thing you need to do is drain the water from the inside using a bowl, I find that the top of a spray tin very useful to remove water from below the filter in the water well.

Bosch Dishwasher Pumps

You will need to access the pump from the front of the machine on this model as the base does not come off, this video will show you how to replace the pump on all these make but can differ from model to model. Bosch, Siemens, Airlux, ATAG, Balay, Constructa, Gorenje, Imperial, Koenic, Kuppersbusch, Neff, Pelgrim, Pitsos, Thermador, Tecnik, Viva, V-Zug,

Possible fault codes are E25, E24, these are drain error codes
Fault Code E20
Symptom: Electrical short or break.
Cause: Short or break causing incorrect resistance in winding of the circulation pump or the motor.
Fault Code E21
Symptom: Circulating pump blocked.
Cause: A blockage between the motor or the pump resulting in insufficient water flow.
Fault Code E23
Cause: As error code E20, but this time the electrical problem is with the drain pump.
Action: Replace drain pump if necessary.
Fault Code E24
Symptom: Dishwasher not draining properly.
Cause: Drain filters blocked.
Action: Clean the filters.
Go to: Why is My Bosch Dishwasher Not Draining?
Fault Code E25
Symptom: Dishwasher not draining properly.
Cause: Possibly blocked filters, as above. Otherwise this fault code could indicate a blocked drain pump.
Fault Code E26
Cause: Water switch/regulator problem.
Action: Check water switch and replace if required.
Fault Code E28
Cause: Fault detected with turbidity sensor.
Symptom: Dishes not getting clean. Dirty water in the tub.
To remove the Dishwasher pump see video and follow these steps

• 1st you will need to drain down the dishwasher.
• 2nd You will need to remove the lid and the side panels.
• 3rd Remove the kick strip.
• 4th Behind the kick strip you will find an access plate this can be removed by undoing the screws and prizing the plate up slightly on either side.
• 5th Remove any of the wiring that might get in the way of you undoing the dishwasher pump.
• 6th This pump is held in place with a bayonet fixing. We just need to depress this clip and twist the pump clockwise on this model (on other models the pump needs to be rotated anti clockwise to release it)
• 7th When the pump comes out you can remove the wiring from it.
  Now you can inspect the pump to see if there are fibers wrapped around it. You can now test the pump with a multi-meter remember the pump in this dishwasher is 54V and is not 240v so don’t try and live test it.