I just snagged a used (but still in excellent condition) Osprey Manta 20 pack recently. The seller did not include the stock 'Hydraulics' bladder with the pack and I need to find something to replace it. I have seen a few shots of these packs and it looks like the stock bladders really do eat up a lot of interior space in the pack. Is that true, or is it just in my head? And if that is the case, what other bladder would you recommend that I pick up for it? I was checking out a Source WXP bladder online the other day, but I don't know if either the 2L or 3L model would fit it. Anyone own one? Do you have any thoughts on using either this particular bladder, or maybe one from Camelbak or some other brand in these packs? Thanks!