..."He's drinking 25 gallons a day i keep a 5 gallon bucket in his reach,"...
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Holy cow, that is alot of water!  Are you *sure* he's drinking five(5) 5-gallon buckets in a 24-hr cycle?  Is he a 'hay-dunker' whereby water ends up everywhere, or is he truly ingesting the amts missing from his bucket(s)?

Is he urinating while he's down, or only when he gets up?  How would you characterize the amount of his daily urinations? (more/same/less than usual)

As for the ODTB cubes, if he has enough teeth to eat them whole/unsoaked, one thing I've noticed is that both of my IRs (one young/good teeth; one old/old-but-decent teeth) much prefer to bite the cubes with their front teeth by pushing down on them on the ground.  I've even watched seen them lift the cube out of a bucket and maneuever it to the ground so they can then press it and break it apart.  Thought that was kinda interesting.  So if your guy is spending time down, he might like a hard surface to press the cubes against, like a wider, flat-bottomed pan etc (again, if you are feeding them dry).  I think there might even be a printed suggestion on the cube bags about feeding at ground level but I dont have a bag handy to clarify.  Anyway, I know you're having a tough time of it so wanted to offer any help I can.  My mare was a little funny about the cubes at first but, as always, once my gelding showed great interest in them, she came 'round. 

Kerry in NY
Sept 2014