Update
Update
Here are some pics of how I implimented Herbie's technique. Yesterday the level in my overflow box went up to the top of the backup drain. So I'm still getting some fluctuations. It's so hard to adust, because just opening or closing either gate valve by a TWINGE makes a difference.
Overflow Box - Drain (with rolled Gutterguard Screen):
Overflow Box - Backup Drain:
- Optimally I'd like the level to stay at the bottom line (that way I get good surface skimming from the intake of the overflow box). The top line marks off where the backup drain would kick in.
Overflow Drain - Gate Valve to Choke Flow Rate:
Update
Here are some pics of how I implimented Herbie's technique. Yesterday the level in my overflow box went up to the top of the backup drain. So I'm still getting some fluctuations. It's so hard to adust, because just opening or closing either gate valve by a TWINGE makes a difference.
Overflow Box - Drain (with rolled Gutterguard Screen):

Overflow Box - Backup Drain:

- Optimally I'd like the level to stay at the bottom line (that way I get good surface skimming from the intake of the overflow box). The top line marks off where the backup drain would kick in.
Overflow Drain - Gate Valve to Choke Flow Rate:
