scuppers

[pair of jacks]

My scuppers are clogged with shards of broken glass from Hurricane Sandy. I removed the screws to attempt to clean them out but the drain top (see attached photo) was extremely hard to remove-I tried to pry it up with a screwdriver and it moved a little but I was afraid I was going to break something- is it adhered to the downward drain pipe? What am I missing?