1.5" vs 2" kitchen sink / disposal / dishwasher drain?

[Manjay]

I've seen arguments that 2" drains clog LESS because they are bigger vs. arguments that 2" drains clog MORE because theres less scouring/swirling action than in a 1.5".
My application has a 3 foot and 5 foot slanted horizontal runs and two 90 degree (sweeping) elbows to the stack. Its vented to a 2" pipe.
What do you think, should I use 1.5" or 2" pvc to the stack?
Thanks

 

[Jeff Handy]

I think exposed drain piping like under a sink cabinet is 1.5 inch, sometimes 1.25 for a vanity or pedestal sink.
If you are talking about drain piping being built in behind a wall, it should be two inch.

Kitchen sink is always 1.5 inch until it hits the two inch tee behind the cabinet.

Unless you are talking exposed plumbing for a washing machine or laundry sink, then I think two inch is ok.

Pros on here might weigh in with better advice.

 

[FishScreener]

The design of waste lines is tricky, and has changed over the last thirty years, as more water efficient fixtures have become the code requirement.

In some instances you need to keep the diameter of the waste line small, in order to have enough depth of flow to actually carry solids, with out them getting stuck on the bottom.

Basically, you should go with what the code requires. There is a lot of work that went into getting to to work.

I remember thirty years ago, one of the hotels on the Vegas Strip remodeled a floor, and a few weeks later started having problems with clogged waste lines. They had installed all new low flow fixtures, and the existing lines were too steep to keep the water from running way from the solids.

A friend in engineering school, who was working his way through college as plumber at the hotel, calculated new grades for the waste lines, and they went back in and did a deeper remodel to re-pipe all the lines on the floor.

He is still at the Hotel and two others, as the director of the physical plant.