Scuppers - back flow ??

[Robert Fowler]

Well I can see that I'm not the only one with mind perplexing problems regarding the best method to exit scuppers on a SF20 being restored. I still can't determine the following:
If I relocate the exit of the scuppers to the transom BELOW the waterline and install RABUD fittings with backflow flaps, will water in the cockpit deck drain out or will the pressure of the water outside the flap (below the waterline) keep too much pressure on the flap and not allow it to open and let the deck water out?

Is there any backflow devise that can be installed on the original scupper design which exits directly down through the hull?

My boat stays on a lift, so fouling shouldn't be a problem with a backflow fitting.