I'd properly rounded off the head on the NRV in the pump tube so no recourse but to remove the tube using a blow torch. On advice I'd filled the tank 2/3rds full with water but was probably too much as the tube wouldn't budge. Emptied out so just under 1/2 was left and tube came out a lot easier. I refitted the pump handle after removing the leather to make extraction easier. There was a lot of solder left in the tank so whoever soldered the tube must have used a lot of it. The NRV looks quite corroded and currently has some penetrating oil on it. Hopefully won't have to drill it out!