I'm actually not that fussed about an occasional sink wee, if needs must, but this is a toilet phobia, and it needs to be dealt with. Sounds like when he's drunk his normal coping strategies (ie the sink) fail him and he just goes wherever, as long as it's not a toilet. So I suspect if you deal with the toilet problem, you might see improvement in the drunk/everywhere else problem.
Is he open to seeing a counsellor? Because that would be my first suggestion and I think the best idea by far. If he's not, is he open to trying to fix the problem himself? If so, one thing you could try is a gradual process of acclimatisation.
Since he's capable of using a toilet sometimes, I wonder if what's scaring him is looking down the toilet, when he's facing it to wee? If so, suggest a sit and wee?
But if that's not going to work, what I'd do is something a lot like what you might do with a DC. Buy a potty. If he finds that demeaning or scary (which he might!) then just find a receptacle that he finds unthreatening and that is big enough to hold his wee. Ice cream container might do, or a nice big pickle jar.
Get him to decide how close to the toilet he is comfortable with being when he wees. Perhaps he's ok standing in 'position' with the seat down? Perhaps he needs to be at the sink? It doesn't matter to begin with. Now, every time he wees, he stands in this 'comfortable' place, and wees in the container. Then he empties the container into the loo. This might be hard at first, and you might have to do it in stages - ie, he may be emptying the container down the sink for a while.
Then, depending how close to the toilet he was to begin with, he GRADUALLY moves closer and closer. Tiny steps, really, nothing that causes a major freakout - just stay at the comfortable level and keep attempting the next one up until it happens.
Aim is to eventually be standing in front of the toilet, with the seat up, weeing in the container. After that, it's just a matter of losing the container.
This will take a while, mostly likely, and he will have to want to do it, and I do think seeing a counsellor would be a better idea - but as a strategy for coping with phobias of all kinds it's fairly common, and I have had it work for me with things other than toilets.