Most new cars can’t be siphoned this way. There is a check valve in the fuel fill line that will prevent the siphon hose from entering the tank.
I pump tanks out by disconnecting the fuel line and affixing an extension hose (sometime not easy due to weird fuel fittings). Then you just need to pull the fuel pump relay and jump the terminals with a wire to run the fuel pump.
One of our caravans (92) actually had an extra hose sticking out of the sending unit that was specifically for pumping out the tank?at least that was the only purpose I could find for it:)