I just got my 5 liter Camelbak system after the cat punctured my 3 liter bag. I found a fish tank tube cleaning brush system- a long semi-stiff plastic rod connected to a soft plastic bristle brush. Feed the rod down the fouled tubing, pull through the brush. Worked great. Check out the pet stores or local fish clubs.
I changed the tube from the bladder to a more flexible tube, connected to a stiff polyethylne section for proper tube placement, then a Tygon brand tube with a large Tygon brand tube PVC glued over it for a tooth gripper. Make sense? The Tygon tubing is softer, gentler on my lips/teeth/gums. The larger tube glued over the normal Tygon tube is only 3/8" long, something to grab on and won't fall out of mouth unless I let it go.
SteveR