Mk3 fabia ..the tail gate door has 3 drain holes but they have 3 rubber Grommets that I thought had holes in them but on closer inspection they are a closed grommet ...so in fact the drain holes are blocked by these grommets ...whats the point in that ??

Well I could be totally wrong but I believe the idea is the weight of the water forces itself out of the holes but the grommet stops dirt getting inside and blocking the hole if that makes sense. 

There's no way water would force the grommet out ...it was hard enough getting one out for the photos. 

The tailgate is a sealed unit. So no water should be getting in there to drain out unless your washer hose fails which I doubt or the rubber hoses at the top that contain the wiring pop off which I can tell you is a right paint to remove / unclip in the first place. 

 

If you removed those grommets and have the boot shut the water that sprays onto the flat part of the rear bumper / where the boot closes too will then allow water into the boot and overtime, could end up with rust.