When I used an additional smaller pump (1K gph) to run my pair of reactors I ran the feed line down into the bottom of the drums and cut at a similar angle to the drums, seemed "spinning" the incoming water against the side of the drums yielded the best boil. Drain was in the side, with a 45, then slit pipe and a cap. Problem was lots of media gathering at the intake.
Flip side you could drain the bottom and dump in the top, using incoming water to help agitate and you should be able to loose some gathering media if you have the air higher up off the bottom then the drain. Drain will need a stand pipe up the side and vent at top so there's no siphon, and to set water level. I never tried this so I'm not sure how much less these style drains flow as opposed to normal ones, so you may need to pipe it a bit bigger then you would normally. I believe you're looking at horizontal flow for pipe diameter as opposed to vertical drains.
I'd rather monkey with drain diameter as a variable then fight media clumping at the drain.....
Another idea might be setting the drain towards the middle, run a standpipe up the inside of the drum then making a mesh half circle to protect the standpipe, essentially making that whole half circle screen guard the strainer. Not sure if it works this way but with that much area on the strainer maybe the media would just bounce right off and not stick? Sounds good on paper right? LOL