Another thread made me think of this.
If you change your own oil or any fluid drains (vehicle, not body) you need one of these. I have used this for years....a mityvac fluid extractor. Works on a vac pump. Simply send the tube down the dipstick tube and suck out the oil. Works perfect and yes it gets ALL of the oil out. It has measurements on the tank, and on my merc, 4runner and my gf civic, it gets out as much as the spec calls for. Just changed her oil yesterday. 45 buck vs over 100 for a synthetic change. Of course if you not a DIY person its not worth it, but I like doing it and I know its right. Yes, you still have to get under to do the filter, but you don't have to deal with the plug and a huge mess of catching the fluid and cleaning a drain pan. The mity vac also works in reverse, so you just flip the valve and you can pump out the contents over fence into your neighbors yard.

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Have seen someone recommend the PELA brand of vacuum oil changers on a Miata forum in the past. Never tried it myself but this fellow swore by it as a way to lighten the work and minimize the mess.

This is great! I just ordered one. I see the Merc mechanics use this too. I assume the dealers may. I have a GL450 that uses 9.4 quarts and the 4R uses around 7. This will make it much easier and cleaner.

Couple things to note in my experience with my merc E550..m278 engine, bi turbo 4.7l v8. I specify because I'm not sure all mercs are like this.
1. The filter was top side so oil changes were extremely easy.
2. The oil dipstick tube was a large diameter, maybe 1/2 to 5/8 inch.
3. When inserting the small tube through the dipstock tube to the bottom of the engine I had a a hard time extracting much oil.
4. I found that on this particular engine, you did not have to get the suction tube down the dipstick tube. Just use the large tube stuck into the top like a cork...the suction will draw 100% of the oil up the dipstick tube. (Open your filler cap)
5. Because the m278 is a dry sump engine you must do it this way. It takes 8.8 quarts (if remember correctly) and it would get every bit out.

So in short, on your gl .....if the suction tube down to the pan does not work, try using the actual dipstick tube as the suction....pm me if you have questions.

Thanks! I appreciate that and will try it soon. I appreciate the tips. Just need my filters to come in. Mine also has the 4.7L engine.

The m278 is a great engine. I highly recommend the weistec tune. I did mine when it was almost new and put over 100k on the tune with zero issues. It was a beast and the only thing that ever beat me was a hellcat. It ran dead even with an r8 v10, and would beat any mustang, 392 dodge.....you know how fast your car already is, it could turn it into a real "sleeper". No negative effect on drivability either.

Mercedes Benz AMG M278 ECU Tune E550 S550| Weistec

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That's freakin' insane AND the fact it's CARB legal. I had no idea that engine could produce that sort of power. I guess I should have as it's a twin-turbo!

Mercedes used the same engine in a lot of different platforms/chassis and would just change the tuning to fit the trim level or platform. In stock form it rated as low as 362 hp in a GL ....up to 449 hp in an S class. so it was built really robust with things like fractured con rods, dry sump oiling....and huge oil capacity.

Why did you get the manual pump instead of an powered pump?

didnt know there was a powered unit...But i can not see any need for a powered unit. This unit is vacuum powered, so you do not need to pump it constantly to create suction. you simply pump the pump about 10 times and let it do its thang. you dont even have to buy it dinner afterwards.

I have one of the evacuators that’s in the OP. These things are great. I use it on a daily basis, and they typically last about 1-2 years. The only thing I recommend is you always clean it out when done. I’ve had it push the oil out of the pump chamber and onto my truck bed several times because I bumped the valve body upward while putting it away. Then the thing pressurizes and makes a massive mess.