There is a tube with a cap on the end. Look carefully for it. You can use a LiquiVac or similar device, and suck it out through that tube.
You could buy a dipstick from the dealer to check the level manually, or simply add the "fill" amount right off the bat. That's what the dealers do.
I uinderstand that some new cars might not have drain bolts. Wonder if the W211 is the first...?
1998 C230 "Black Betty"