I spent a lot more time, strategy (and money) on this one. Been sawing like crazy. I had not idea that speed was important to the drain, but was well informed with my last post. OK, here's the new one (SWMBO snuck her hand into the picture).
The face down thing is for 2 reasons but I'd say it doesn't really mater.
If the slot are below the level of the spigot and you have a tube on the outlet you will have a siphon effect going. But in reality this probably won't happen because your fittings won't be airtight and your slots will go close to half way or past. So the level won't be any difference than if you have them on the top.
Then there is husks blocking the slots on top but because the slots are also at 90° on the tube this won't matter.
I don't think I've heard of anyone with a slotted manifold getting a stuck sparge. The seem to work well.