if i'm thinking of the right fuel retriever unit then how do you goet over the anti-syphun mechanism built into most filler necks these days.

The one we used to have had a pipe you inserted down the filler neck, then it had a large rubber seal that sealed off the filler neck opening then you manually wound the pump hand round to casue a vacuum but it never worked and was a complete waste of money and time.

Electric fuel pumps connected to the fuel supply pipe seems to work or as mentioned bridge out the relevent fuel pump terminals and let the intank pump do the work.