The Note is saying this in Mercedes engineer speak:

The "Actuating Button" is the White Plastic Knurled [It's knurled so that you
may loosen the "Button" (Lefty Loosey)and "pump like mad"and then secure the hand pump by depressing it fully and tighten it by screwing the "Button" down
(Righty Tighty)] pump handle.When you Tighten it it seals (Allegedly)the hand
pump against air leaking in.

The bolt on top Center of the Secondary (spin On ) fuel filter is hollow and is sometimes referred to as a "Banjo bolt".In fact ,if you'll look at all the bolts
on the Fuel filter housing (Secondary,Spin On) to the Right of the dead center
bolt securing the Fuel Filter they are "Banjo Bolts" also.

If you've pumped enough so that the fuel is coming out the vent bolt...
(and you've taken care of all those other things) you're ready to start it.

(In your picture the top radiator hose is disconnected)

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'84 300SD sold
124.128