Overflow box empties to fast.

[2bafish]

Originally Posted by Aquattro

You simply need an air hole at the top of your plumbing. Don't restrict anything. Look up durso design, it shows how to use a hole with a valve. I don't use a valve myself, just have a small air hole in the top of the stacks (dual overflow pipes).

That was it. Thanks for all your help. So simple but effective.