5Series,
Do check yr fuel pump seals, they shld be leaking. When yr tank is full and seals leak, the fuel will splash (kinda spurt actually) out the loose/broken seals, due to the pressure. When its down to 3/4, the fuel will not reach the top of the pump.
Also, do what Affan suggested, check the hoses too. Do it as preventive maintanance while u r there ma....
Let us know yr solution, damage to wallet, ok??