It has been my experience that a 4" diameter vertical pipe of 3 feet or more works fine.
The waste foam collecting area needs to be big enough for time for the bubbles to rise up and form foam.2. At the tee, is it better to narrow the waste exit diameter at the water level or immediately above it? In other words, is the narrower exit supposed to facilitate the foam to exit more quickly or is it supposed to decrease the surface area of the water at the tee? For example, I noticed in the 4" PP design that the waste exit has a 2" reducer bushing but the water level is still at the 4" part. However, in the 6" PP design the water surface is 4" in diameter and not 6" with a 4" reducer above it.
The foam needs to push up to exit. 2" foam exit seems to work best for me.
If you mess too much with Ethan's design and do not get foam... then you need to build one that looks like the examples posted that work.3. I noticed that the water level gurgles and oscillates a lot in the tee, which prevents me from setting the water level very close to the exit. Flow is about 1200 gph following Ethan's 6" PP design. Any ideas to reduce this?
Any comments on any of the questions would be appreciated!
Then once you are getting foam... you can experiment with modifications.