Difference between 1.5" and 2" drain in overflow

[christyf5]

Originally Posted by sphelps

The 1.25" pipe goes all the way through (it's one piece) and acts as the secondary or back up drain. It's supported inside the 2" pipe by the bushing.

The primary drain is created by the 2" pipe. Water flows in between the 2" and 1.25" pipe and then through the gate valve. The gate valve is used to match the flow rate to the return pump and adjust the water level in the overflow box to just below the top of the 1.25" pipe. It's just like a standard herbie but the back up drain is inside the primary.

Make sense?

Yep we use something like that in our tanks at work (DFO), only the "inner pipe doesn't go all the way through, it sits in the bushing and has a hole in it at the level we want the tank at, reducing the flow. To flush the tank we pull up on the inner pipe and the flow is increased dramatically and sucks out all the detritus.

Cool, thats definitely something to investigate further. Thanks for the info!!