I recall the discussion on DC, but unfortunately their search function is disabled so it would be difficult to search for. It was at least a year ago, probably well before that.
That question is one I've never had a firm opinion on, but the suggestion that Ennis hasn't dreamed about Jack for awhile was one aspect I'd never thought of. One part of the other discussion I do remember is the mention of the sound of the wind being like shovels full of earth. (? ? ? my copy of the ss doesn't include the prologue)
As far as pissing in the sink is concerned, IMO if this has any significance it's to underscore Ennis being alone, and having been alone for some time. And you can add to that the fact that in the country, taking a pee outside when Nature calls unexpectedly is much more common and practical than in more populated areas. For someone who lives alone, at least a man who lives alone,* I guess it wouldn't be a very big step to piss in the sink right after waking up rather than bother with the bathroom.
*For a woman, peeing in a sink might iinvolve climbing up on a chair!