It's just an empty tank, but the outlet comes from a pipe that goes to the top. It'll drain out if you can disconnect the solenoid valve on the inlet, or some have a safety valve for excess pressure at the bottom, that might be removeable.
Thanks. Taken the old Triton 8.5Kw shower off and have it sitting around the garage trying to get the water of it. In the diagram attached from the manual, the inlet is (1) and the shower hose connection is (15) at the bottom.It's just an empty tank, but the outlet comes from a pipe that goes to the top. It'll drain out if you can disconnect the solenoid valve on the inlet, or some have a safety valve for excess pressure at the bottom, that might be removeable.
What's 11 in the diagram? It looks like it might be the pressure safety valve I referred to, and looks like it can be dismantled.