Questran and Welchol (what I am on) both absorb excess bile. It keeps me from having D after having my gall bladder out. Yes, by all means try one or the other of them. In fact, I'd try them before I had any more tests because bile is most likely your sole problem and testing to look for some other problem is likely to be fruitless. (That you only have ever seen blood once, and that was months ago, makes it sound like a temp hemmie problem.)
Having bile D after having your gall bladder out is VERY common and there's nothing else to be done for it pretty much except to take the medicine (sometimes altering diet can help, but it sounds like you're not getting anywhere with that). That you get D when you drink water makes it sound like you are pretty severe. My m-i-l was almost that bad; as soon as she ate anything, she got D, no matter what it was that she ate. She's now on the Welchol too and she says it's like a miracle for her. We both have some D problems when we eat things we know we shouldn't, and I especially seem to be more sensitive now to antibiotics and other bugs floating around--it doesn't take much to upset my gut--but, by and large, I have MUCH less D than before, and it's more predictable when I have it. I'm not as bad off as most of the people on here.
Technically this is called post-cholesectomy (sp?) syndrome and isn't really IBS; PCS has a cause--lack of gall bladder--whereas IBS has no known cause.
My m-i-l and I are both overweight, so having D frequently doesn't necessarily cause you to lose weight.
You might also benefit from taking Caltrate 600 w/vitamin D. That is naturally constipating and can help when you have D. That's all Inape uses to control her D, but you sound like such a severe case, I think you will still need the prescription med. I use the calcium too so I don't have to use quite as much prescription medicine (also, I think the calcium keeps my digestive tract healthy; it certainly calmed it down when it was hurting bad a couple of summers ago).