Staying properly hydrated, you may find 2 liters of either drinking water or urine storage insufficient for a typical day of flying. For me, 4l is a minimum.

A suggestion:
Drill a 1/2" hole in the belly aft of the stick. Bond a 1/2" OD 3/8" ID Polyethylene tube flush with the belly and long enough to pass through the seat pan aft of the stick. A short piece of surplus Mylar on the belly can seal the hole when not in use.
Use a 5/16" OD Poly tube for the part actually carrying liquid. It can easily be retracted for low drag (also clearance for takeoff and landing) and extended for use.
Use the female part of the quick-connect (McMaster, Wings and Wheels, etc.) on the PE end (may require a short piece of more pliable tube).
Use a more flexible tube with a barbed inline fitting on the other end to connect to the catheter.
Nothing wet in the glider. Empties beyond the laminar flow so very little if anything to wipe off the belly after flight. No bags in the cockpit or dropped outside.
Unless used during a low pass or above another glider (oh, you'll pay for that) the rain will evaporate. Not being concerned about filling the bags will let you stay better hydrated.
Jim