Downsizing outflow pipe at wall

[DavidS]

Hi, I have a dishwasher that needs to move further back to fit flush with the other units, as is sticking out.
What's in the way is an outflow pipe with 50mm diameter. Replacing it with a 25mm pipe would do the trick.

Pic at pipework.png hosted at TinyPic - https://tinypic.host/i/ocehtd

Questions
1. Is this feasible?
2. Do I need to replace the whole pipe in the wall or can I get a converter (hoop shape) 50mm to 25mm?
3. Where can I buy a single simple part like this?

Many thanks in advance from humid south London

 

[SimonG]

It shouldnt be connected like that anyway.
Where does it go to once outside? a gully? hopefully not a stack.
Is dishwasher next to kitchen sink? If so could use an appliance trap and do away with that pipe altogether.