Decided to drill my tank

[CM125]

Should generally aim for about 6" between the siphon tube and the overflow, less will work but can be harder to tune and will take longer to recover on restart (this is why people use turned down elbows, to get the siphon tube lower). The second picture would work, but if you can get more height I would go for it

[CM125]

http://gmacreef.com/herbie-overflow-...method-basics/

[Easto]

I was thinking about drilling near the Middle of the overflow Box height. Then putting the siphon tube with the elbow facing down. I haven't measured but I'd think that would give 1.5" - 2" between the siphon and the bottom of the box, which sounds like it's fine.

The second one I'd drill at the same height but turn the elbow up facing.

[CM125]

I would try to get more space then that, even if you add some pipe on the top or bottom, it will fluctuate a lot in the beginning and its nice to have that extra. since you have the option I would definitely do it.