It's normal for the tank to hold minor pressure (hence the instructions in the owner's manual to vent it before removing the filler cap), so do yourself a favor and take the cap off. Keeps the mess down.

As to the hand pump, the seal on the piston is also the closing seal -- if it leaks fuel out while pumping, it will definitely leak air IN while running. If you get any restriction in the line or tank screen, you will "run out of fuel" when it sucks in enough air, and it will be a HUGE PITA to get started again. BTDT.

The replacement is a sealed version that you just push down on, no unscrewing, etc. Take a look on Fastlane on this site.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!