When to transition lift pipe from 2" to 3 or 4"

[PapaDisco]

At what point do you transition a lift pump line from 2" to 3 or 4"? If you have a long horizontal run after the lift, and the run has the correct pitch, then why not make the horizontal piece 3" or larger and let gravity do the work? Or is it better to run the 2" pressure line all the way to the stack?

 

[James Henry]

The purpose of a lift station is to lift deposited waste to the nearest available horizontal gravity drain. So you knew the answer all the time.

 

[Sponsor]

 

[PapaDisco]

Thanks for that confirm James. Is there an ideal way to finesse this transition? A simple bushing gets me from 2" to 3", but that may be conducive to sludge formation? I thought of bringing the 2" in via a long sweep and capping the 3" end as a cleanout.

In the future, I'm remodeling a kitchen and intend to add that flow as far upstream as I can to this drain (within a foot of the 2"/3" transition) so that there's more scouring water flow to move the septic lift material along the horizontal.

I've googled the heck out of this subject and have been surprised at the lack of information. Lifted septic material has got to flow very differently from traditional gravity flow, particularly lift systems with grinders (mine is not). You'd think there'd be a different science to the pitch and layout of this combinations.