Revisiting Transom Scuppers

[oldfielder]

I'm entertaining the idea again of running my drains out the transom. Generally, I am happy with the deck drains, but there are some applications where I would like something that drains faster.
So far the ones I like best are the Gemlux with the flapper(Capt. Chuck's application) , but I have a few questions:
1. What kind of pitch do I need from deck to thru-hull for a good drain, even at rest?
2. Is it essential that this kind of scupper be fullyabove the water line at rest? I am sure there is a simple answer to this one, but it's not coming to me.
3. My harbor is fairly productive on the marine growth side, so I am thinking the ball scuppers may be a PITA maintenance-wise.

I know this topic has been beaten like a dusty rug, but I still welcome specific answers to my queries.
Thanks.
Oh yeah, Happy Easter