Thanks for all the advice. I did as gasmick2 suggested and clamped the larger bottom nut with a mole wrench and then borrowed the largest stilson wrench that would fit in the space available to use on the top 3/4" fitting.
It still put up an almighty struggle but the extra leverage from the...
I am trying to plumb in a power shower and would like to fit the appropriate flange to the top of the hot water cylinder. I have disconnected the pipe from the top of the HW cylinder but am left looking at a 3/4" male thread fitting:
I suspect the male thread is an extra fitting that is...