how do I clear drain in battery compartment / flooded footwell

2003 passat wagon I've found that the reason why the footwells in my car have been flooding is because the windshield drains into the battery/master cylinder compartment, and the drains for this compartment are clogged with debris, and are concealed out of view under the battery or the master cylinder. This compartment fills with water, which then enters the cabin through holes in the firewall.

Can anyone tell me exactly where these drain holes are so I can clean them with a stick? I want to resolve this quickly, because I'm told there is some sort of computer module under the right side floorpan which can get ruined. $$$ TIA