I normally use a regular 1 or 1.5 liter Nalgene bottle when caving. The 1.5 is great for warmer climates when I need to hydrate more, but I tend to deliberately under-hydrate myself a little when caving. I prefer not to carry my own pee out unless I really have to go.
(I carry a little rolled up Platypus bag which I can use for that if necessary.)
I cave with the large Swaygo pack
and yes, it would be tough to roll it closed properly with a tube hanging out. I once tried using a hydration bladder and tube when caving with my old Lost Creek pack, but I just found it too awkward. I've seen other cavers with hydration tubes hanging out, but not very often.
For above ground hiking etc, it's a different story. I love my current hydration system, but it took me a while to find one I was really happy with. Since you opened the door and mentioned Camelbaks
here's my 2 cents. I've gone through a few generations of Camelbak, including my last one which is the black 3 liter military-type HAWG with the modular Hydrolok attachments. Camelbaks have never really seemed taste-free to me, and my older ones progressively got worse and worse even with proper care. The military one I got about a year ago is a really nice looking setup, and I desperately wanted it to work for me. Alas, no matter how much I told myself that taste didn't matter, that particular system (purchased brand new and sealed) was positively vile. It tasted like rubber.
Anyhoo, while trying to reseach options for trying to remove the taste I stumbled on the solution. A different brand of hydration bladder! I now own a couple made by
Source Vagabond, an Israeli company which makes a nice taste-free system incorporating a layer called Grunge Guard. So far, it's working great. They can be found marketed under the name
Deuter. Note that with most of these models you can open up the whole top of the bladder, making a it really easy to fill it and also to clean it. Source also make models for the US military under their own brand. I have a 3 liter one of these, and a 2 liter one which came in a High Sierra brand backpack.
There is one possible downside with these. The bite valves are a different design from other types, and in some cases they have been known to develop a slow leak after prolonged use. People sometimes choose to replace them with standard Camelbak valves or other types. The parts are generally interchangeable. I was happy doing this switch with my 2 liter model, but my 3 liter military system works fine using its original valve - a new simple design similar to sucky tops on bottled water containers.
So in answer to your original caving question, you could maybe try a non-waterproof type cordura caving pack like a Lost Creek model. Then you can put dry bags/cases inside it for those items you need to keep dry. The top of the (non-waterproof) pack can then be rolled down and secured with your hydration tube hanging out the top. You could even thread it though the brass grommet that many of these packs have in the bottom as a drain hole. You could also shroud your hydration tube with tubular nylon webbing and get a bite valve cover (if you don't already have one). I'd still find it a hassle to have a tube hanging out while caving, but to each his own. Good luck!