6 April 2012: Repair work on the Sunbox is progressing. The leak was coming from the plastic piping between the two sets of panels, and it is impossible to repair the old Tee-Joint. I would not be able to obtain a replacement on a bank holiday, and even if I could, I would not be able to re-insert it. The space is too small and it was a nightmare getting it in in January 2010. So for the new external piping, I have taken the risk of getting 40mm waste drainage compression fittings - normally these work with gravity, so aren't used to pumping pressure. They are polypropylene, the same material as the black panels, so they should be strong enough. The Tee is designed to be helpful to gravity, so it is asymmetrical. The asymmetrically helped as the vertical centre pipe is not precisely central - it now fits perfectly. Our system is pumped, so this small rightward bias will not matter. The fitting is shorter than the previous, so it is easier to fit in, although I might get some replacement rubber hosing (longer and thinner skinned) before finally closing everything up.
(to compensate the poor birds, we are fanatical about feeding them, providing sunflower seeds throughout the winter, and bit of waste meat or fish throughout the year. If the cat won't eat the waste, then it goes to the birds.)
So this is what the Sunbox looks like, seen from the field at the rear of the house. I now have some internal plumbing to do before these can be restarted. People walking past the house now have an answer as to what is inside the Sunbox! The external piping is done as best I can, but the loft space requires an expansion bottle, pressure gauge and drain point.