Is draining Dogger bank a good Idea?

Can't drain it, because it is below sea level. It will come to surface again if/when major glaciation occurs.

How do you drain part of the ocean...

That's a lot of water to move.

We've looked into it a number of times, including the idea of building an airport on it. However, the potential reward has never justified the cost. Maplin Sands would be a better concept.

Presumably you're asking about draining the North Sea, or at least part of it.