you CANT clean your drains properly, or even anywhere close to ok from the top, so dont bother..
the L shape covers you talk of are the top of the hardtop prep kit.
As im a nice guy ill repost what i said a week ago...
Jack up wheel (you can take off the wheel if you dont have monkey hands)
take off the front arch cover, there are 3/4 screws i think, some under the car. (you DO NOT need to take off the whole lot,)
Put you hand in and unscrew the plug, its black and squidgey.. you can see it with the plug removed here. that hole.
Shove an 8mm plastic tube up the hole, squirt water and suck etc, attach hoover etc..
You can also reach the drains by putting the hood up, and sitting in the seat looking over your outside shoulder, you can see the top of the drain there.