In article , "Steve
Harris" says...
Every few years, my immersion heater element fails and I have to replace
it. It's a bugger because "draining" my hot water system doesn't
completely drain the tank. The element is still immersed and I gently
undo the element until the thread leaks and shove a bucket underneath.
It then takes hours to drain to below the element. There is no drain
cock for the cylinder.

1. Does anyone know a "Trick of the trade" to do a easier job of
draining the cylinder?

I'd have thought that applying air pressure to the vent would force
water back up the cold feed and into the header tank, where there is
presumably some sort of overflow pipe, but it's not something I've
ever tried.