The thing that has two big and one skinny hoses connected to it is the
fuel pressure damper.  One big hose feeds into the intake of the fuel
pump, the other is coming from the fuel tank.  The purpose of the
skinny hose is to give fuel that might leak through a defective
accumulator diaphram someplace to go, i.e., into the  low pressure fuel
supply.  If you disconnect  the  skinny hose, fuel will run out  of the
damper until  your  tank is empty or you clamp/plug it.  To test your
accumulator, disconnect the skinny hose from the accumulator and plug
or clamp the hose.  Connect another hose to the accumulator and put
the other end of that hose into a container.  Start the engine.  If
there is  fuel coming out of the hose connected to the accumulator,
replace the accumulator.   DO ALL OF THIS OUTSIDE WITH A FIRE
EXTINGUISHER HANDY.  If your accumulator is ok, you have a
harder-to-diagnose problem.  Let us know.

I  suggest that you  post your questions directly to
http://groups-beta.google.com/group/alt.auto.mercedes rather than
through carkb.com, since carkb.com is simply grabbing this newsgroups
posts.  Also, get a service manual (currently available only on CD).
E-Bay has them.