Definitely cut back on the milk. If you don't want to cut it out all at once you could give him less and less over a period of time or you can simply give him his milk earlier in the evening. I would also try sitting him on the potty just before bed. He may not get it at first but once he goes for the first time not only will he go less at night, you will be well on your way to potty training!
This seemed to work pretty well for me. I have two daughters so I don't know how it would work with a boy. My girls usually get a bath before bed and before I put them in the tub they go potty. I started this around 18 months with both of them. My second daughter just turned two a few weeks ago and is already potty trained...with occasional accidents of course!
You could also try training pants...I think they make a special night time version.
Good Luck!