Thank you Derek
Yes it is a submersible. It is amazing how much strength you can generate by losing your temper. I wrenched it out of the tank. But It is near impossible to get the new pump in. I can only get one hand through the inspection hole and cannot see a thing. Also, the updated pump is 4cm shorter than the original so I will need to connect it to a hose so it so it reaches the bottom of the tank.
The joys of motorhoming
Barry