
Consistence and a LOT of patience! :D
How long have they had him? Going to a new home is a traumatic thing for any pup, they've gone from littermates and mum to being by themselves (most of the time) in a strange place. It is very daunting and stressful.
As Perry says, getting pup into a routine is the best way - and dogs love routine, he should pick it up in no time. When my middle two were pups, if they cried, I'd take them outside to make sure they didn't need to do anything (including poo, not just pee), and if they kept going I would ignore them. I had the cage next to my bed so they didn't feel totally alone. Look at it from pup's POV: imagine if you were plucked from your family and put somewhere completely unfamiliar and left totally alone, in the dark, with nothing familiar around you - you call for people, they come and let you out, then disappear again in a short time - how would you feel?
I didn't use a crate for Opi - I had her in a puppy pen at night for the first few weeks, then she slept loose downstairs. She was one of those pups that just would not accept being crated at night - no trouble during the day, she could be in there hours and no problem but not at night. Even now she'll sleep in it if it's up (she's 4), never did figure that one out!