I've noticed a lot of small leaves going down the small vented drain holes at the bottom of the rear window but cant find a way to remove the cover and clean out what must be years of accumulated rubbish . Has anyone managed to remove this or tell me what happens to all the rubbish ?

 

All I do is make sure that those drain holes are clear. Then I run some water from a hose into those holes and ensure that the water is draining to the outside of the vehicle. Then I know that the passages are clear.

 

the water comes out ok but there has got to be a whole lot of rubbish compacted in somewhere with the potential to cause rust . None of the debris seems to come out and the holes are pretty small

 

Fair enough. What you could do, is pour some undiluted Simple Green into the drain holes, let it soak and sit for a while, then run a high-pressure stream of water into it. You'll likely see some grungy debris come loose. There's also a product (here in Canada anyway), called "30 Seconds". It removes mold, mildew and algae etc from roofs, siding sidewalks etc.