My word, thanks for all the input, chaps. Harry, yes I am unless I decide on a weekend in Poole; service Saturday, fish Sunday. Rich, don't make me invoke the Dark Forces; scoff at your peril!
For the others, I'm not actually replacing the existing one, I'm fitting another one to accommodate the inlet pipe and cable from the exterior bilge pump to the bait tank. But I will remember the advice when I do have to.
Terry.