After paddling a G2 Ion at Gorge with the old-style Think drainage system you describe, I would say just leave it as is. With the plug in, it's totally dry which is nice in flat water. With the plug out, the drainage rate is totally fine for slop/ downwind.
The new bailer on the G3 boats isn't totally watertight when closed, so every few minutes you have to kick it open to drain a bit if you don't want water sloshing around your feet. And the fully open position drains a monstrous amount of water quickly, but I never need to do that when paddling. So I usually just leave it open a tiny bit and leave it there, which is essentially the same thing as having a venturi.
You might be able to improve the drainage and reduce drag on the venturi by adding a bullet, here's a link to a geek-out thread regarding this option:
www.surfski.info/forum/2-announcements/1...placement.html#20609