Yes, it's confusing isn't it! I've also come across recipes that call for drinking the oo/lj WITH each meal and then again before bed.
Re the pressure idea.. surely drinking a lot of oo as we do in the flush is going to put pressure on the liver to produce and shed it's load of bile? Also, even eating fat for brekky and using up some of the bile doesn't mean that there will be less of it when the oo comes along!
At the end of the day you gotta go with your guts, I guess and everybody's guts will give them slight or profound variations. The protocol, when some prefer to stick to it rigidly, is probably working for them. But even the professionals who've used one protocol for x number of clients cannot honestly say 'this is the way to do it; period'!! I think we can get hung up on 'the right way' and attempts to explain it take us into ever more complicated mazes. The basic idea is, a load of olive oil will stimulate the GB (and eventually the Liver) to release it's contents, (perhaps more dramatically than castor oil, I don't know.)