As for the filling rate, you can control that with the separate shutoffs on each outlet.

Now as to your siphons, if I am seeing them correctly, they seem to be a "T" elbowed toward the bottom of the tank with two open ends at the bottom. Too much open end causes loss of suction too quick. Do away with the "T" and make it an inverted "U" with the open end of the drain a distance from the bottom of the tank of about 1/2 inch, no more.

This new version of this site is killing me too.
Sorry about what the new owner has done. I had purchased this software a number of years ago thinking I would update but decided against it as it didn't seem to have the personal community feel to it as the what I had been using since day one. Sorry.

Hope my suggestion helped.

JCO