Herbie overflow - what size?

[MikeInToronto]

Both the Herbie and the Beananimal work best with a coast to coast overflow. You want just the surface tank water to enter the overflow and you want it to "hug" the sides of the overflow as it goes in. Otherwise you have a very large volume of water being pulled through a (relatively) small overflow box. This leads to a lot of problems with fishes or other animals getting sucked over the weir, or it results in a loss of efficiency as the overflow no longer pulls just the surface water. Therefore, a properly set up overflow for a Herbie will be large enough for a Beananimal as well.

I would go 1" as a minimum for your open channel and 3/4" for your siphon. If you are going with 600 gph, I'd do 1" and 1" (and 1" for the Emergency if doing BAA).