I think Transair and some of the other pilot retail shops still sell the 'Little Johnny', along with 'Lady J' adaptor.
Personally, a plastic water bottle or old coke bottle does the job just fine.
I do remember one particular glider trip, where myself and my flying buddy that day ended up playing pass the bottle on several occasions. We'd been airborne for somewhere in the region of 6 hours, enjoying ourselves at nearly 20,000 feet in the most spectacular wave.....absolutely no way were we giving up and heading for terra firma with such fantastic lift around!! Thank goodness most gliders have a DV panel on the canopy where you can stick the bottl out the window and chuck any unwanted 'water ballast'!!
