Shower Valve Cap

Well, it's that time of the year when we like to go Camping, and after a smelly evening in front of a BBQ and spilt beer we need a shower, right ?.
So off we go to the shower block and into the shower cubicle, to be faced with a push vavle on the wall that gives you enough water to water a small plant, before it pops out and off we go again - press the valve and another small dribble of water appears, it's enough to give you RSI.
So, print this little device that I designed, slip it over the