I could not find any specific info on this procedure for this car so I will post from my experience and anyone else can add comments if they wish. This procedure is for the 1998. I assume it is the same for 1999 also. Any other years I don't know for sure.

There are 2 drain locations: Radiator and block. The radiator drain is on the drivers side (US) of the car at the bottom of the radiator. There is a little nozzle where you can attach a 3/8" or 7/16" ID rubber/vinyl tube. 6" length is good if you are going to catch the liquid in a plastic milk jug (1 gal). There is a little red knob to open the valve and it uses a large blade screwdriver. You need to remove the engine under cover to get to this. The engine under cover is held with 4 screws. I used a 5/16" nutdriver for these but they are technically 8 mm.

I was able to drain 1 gallon of coolant from that drain location.

The second drain is the block drain. It also has a little nozzle on it but it takes a 1/2" tube. You will want that one longer, about 14" probably. That one loosens with a deep 19 mm socket or a 3/4" works good also. It is located exactly where you cannot reach it from top or from underneath and definitely not if the exhaust manifold is hot! It is located beneath the exhaust manifold between #3 and #4 cylinders. I was able to drain 1/2 gal from there. If anyone knows an easy way to get to that drain let me know!

That left 1 gallon still in the system. So I had to puzzle on how to get that out. I thought about maybe running the "rest" circ motor but could not get the connector off. I thought about maybe disconnecting other hoses. Finally I added a gallon of distilled water and ran the engine for a minute and then drained that out. It came out the same color as the other coolant, so I figured no matter how much water I added I would still have some old coolant in there. So I figured I had to choose between flushing it with the hose and leaving some tap water in there, or not flushing it and leaving some old coolant in there. I went with option "A". I put the hose in the filler hole and turned it on just as much as could drain out of the radiator drain. Then I ran the car with the drain open. I should add that I had removed the thermostat for this procedure as recommended by Haynes (put the housing back on with the thermostat removed). The water eventually ran clear, then the temp went up and then the water ran darker again. Keep in mind the thermostat was out so I don't have an explanation for this. Anyway, after a while I decided all the old coolant was out. So then I turned off the car and removed the garden hose.

Then I opened the block drain again, drained everything out then closed both drains and installed my new thermostat. Then I added a gallon of G-05 and 1/2 gal of distilled water. I drove around the block and the add coolant light came on so I added about a quart more. Thats it!

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Hey, thanks for the write-up! I'm about to do this with my 2000 C230... how did you get to that engine block drain? I took a look at it last winter and couldn't see an easy way to get to it. I'm vaguely tempted to just drain the radiator and put in a gallon of 50/50 mix.

That was pretty bad of me not to say how I got to it!! I think from the top which is why I made the comment about the engine being cool. I think I used a long extension on my ratchet. Sometimes universal joints work on these problems. I got a 3/8" impact type universal joint that works really well. I don't use it for impact, it just works better than the old kind of universal joint. It is black and has kind of a ball joint in it. Anyway it is possible and is well worth the effort to drain everything as good as you can. I had to flush the system to get all the old coolant out so using distilled water is basically out unless you have 20 gallons or so. Be sure to use the correct coolant which I think is the Zerex G-05 for your car. Or the Mercedes brand from the dealer. Same stuff, light yellow.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra