SLK blocked drain tubes - take 2


Active Member
Jan 23, 2005
the wilds of Lancashire
2006 SL 350
Further to yesterday's query about these tubes - I've sorted it.

Thanks for the comments - and yes, I have waterproofed the pump. And I check the drains for blockages regularly.

So, for anyone else who might need the info, this is what I did. The ends of these drains (there are two on the right side, one from the boot lip and one from the fuel filler) aren't visible under the car, but it's fairly clear that they run down the wing, behind the hydraulic unit and exit somewhere just behind the rear wheel. To see just where they exit means removing the boot trim and the roller blind (two bolts). All the trim fasteners apart from one are push fit. First the side to side piece around the boot catch, then the roller blind, then the side piece covering the pump and hydraulics - at this point, the trim won't come out because because it is fitted round the boot hinge. So next tape down the roof microswitch on the right of the boot, close the boot, then open it from the front using the roof switch. With the boot open, but before the roof starts to move, you can now remove the boot side trim.

All is now revealed - the tubes pass down the wing at an angle of about 45 degrees to a point about 4 inches below the hydraulics. Then they turn through 90 degrees and exit into the space between the rear wing and bumper. And the bend at the bottom is what stops attempts to clear a blockage with a piece of wire - it won't go round the sharp bend. And too much force with a sharp piece of wire will puncture the tube - and let water into exactly the area it must be kept out of.

However, if you look behind the rear wheel, there are two bolts with caps holding the bumper. If you feel into the space between the bumper and the wing behind these bolts, you can just feel the ends of the drains - but you can't get at them. So what I used then was a length of 3mm diameter wire rope, greased the end with rubber grease and fed it down the tube from the top, twisting it and squeezing the tube at the bend to get the wire round. Eventually, out came a lump of stone about 3-4 mm across, a load of grit and some very dirty water.

Half an hour's reassembly, and job done.

Also of note is that there is another drain in the bottom of this area of the rear wing which exits downwards behind the rear wheel as a 1 inch diameter rubber tube. As long as this drain is clear, it isn't obvious how water can collect around the pump, even if it gets into the boot.

Hope this helps someone else.



Hardcore MB Enthusiast
Oct 5, 2006
Dorset on South Coast
R230 SL500
Re waterproofing the pump, this is a very difficult thing sometimes, having discussed these things many times with MB engineers we never know what to say or do, nothing could be worse than water getting in, but cant get out.
Some of the foam blocks used are hardly the best things to put them in, when they act like a sponge. If one can put drain holes at the bottom,so much the better.

On my SL, I have punched drain holes in the bottom, just in case

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