I usually plug lines like that with a plastic golf tee. The fuel can also be stopped from siphoning from the tank by blowing enough air back through line to push the fuel back into the tank.
Dutch
2001 GBM Landau 34' Class A
F53 chassis, Triton V10, TST TPMS
Bigfoot Automatic Leveling System
2011 Toyota RAV4 4WD/Remco pump
ReadyBrute Elite tow bar/Blue Ox baseplate