Re: 4" pipe to big?
Yeah I have to agree with the others in that you need to stick with the self-scouring principal.
A couple of years ago I attended a week long educational class which was based on both the UPC and the IPC. The neat part is it was held at the Union Hall in Las Vegas. This place is second to none for teaching but the part that was interesting was there was a first floor classroom built directly below the upstairs men's restroom. All of the plumbing for the upstairs bathroom was run in clear PVC so you could watch the action of the water at different fittings. The vertical waste line dropped to just above the floor of the classroom then ran horizontal the full width of the classroom. At least 80% of the time the low-flush water closet was used it abandond solids in the 4" line.
If you ever make it to Vegas try and get them to take you for a tour.
"Somewhere a Village is Missing Twelve Idiots!" - Casey Anthony
I never lost a cent on the jobs I didn't get!