I believe that's the drain tube from the air cleaner's oil separator. The turbo drain is underneath the turbo.

In the future, post Diesel related questions in the "Diesel Discussion" section of this forum, it is 5x more active and you'll get a lot more response a lot quicker!

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)