This was my first design. I was looking for minimal intrusion in the tank, so rather than useing bends, I placed a smaller diameter tube into a larger one. I estimated the cross-sectional area balence of tube sizes really poorly. I also needed to have the outlet over flow point lower to effectively increase the simulated head ability. Basically, this one works great for low flow levels, (like your fluval), but saturates and cant keep up with big pumps. For a fuge though, less flow can be a good thing.
The cost was about 11$ in plumbing junk, assembled with superglue in about 30mins of cutting, fitting and glueing.
This next design intrudes into the tank much more, but it handles all the flow i can throw at it easily. I was not able to saturate this overflow with a 1/4hp pump (operateing under 4ft head). Its bigger, bulkier, and more of a challenge to initially prime, but it does its job like a champ, and thats what I like in a tool.
Its cost was about 15$ due to the price of all the 90deg elbows required. It took quite a bit less time to build, also useing superglue for the bonding agent.
Neither unit has ever drawn air or malfunctioned. Both are nearly silent, the only sound i hear comes from the water entering the fuge, which I later silenced with a corse spounge in the return tube.
I hope this helps you!