Hi Gurney - I can access the tank and outlet pipe, so don't think patches are required. As you say drinking traces of petrol won't kill you. Oral toxicity is low. It's breathing fumes that is dangerous. - Health Protection information sheet.
Steam is a sensible idea which I was already considering - should evaporate and flush any petrol traces.
I am also well aware that petrol can degrade rubber and that the pipes and pumping system would need to be cleaned thoroughly and checked properly. I am looking at possibly upgrading to a battery operated electric pump, so may just replace the lot.
Quack!
Geoff.