Sounds as if that contractor is conscientious. But the IPC permits minimum 1/8 per foot for pipe 3" or 4". Greater is good. I would use the 1/8" before using a pump to get the 1/4". Perhaps 3/16" would be possible for gravity flow.

IRC and IPC both permit 1/8 slope per foot of run.

Greater slope is not neccessarily a 'better' slope since some plumbing scientists/researchers think that the greater the slope the greater the chance for liquids and solids to separate...and therefore for solids to be left behind to 'clog' pipes.

There is also nothing is any plumbing Code that would prevent 'multiple' pipe slopes.

That is: There is nothing to prevent, say, the 1st 150 feet of pipe to be sloped at 1/4" per foot, then to have the last 100 feet to be sloped at 1/8th inch per foot.

Peronally, I would eliminate all the cast iron pipe and go all PVC....using the slopes set forth above...

Your contractor is not impressing me with his 'knowlegde'.

He sounds more like a "hack"...

The IPC (2006) (704.1) specifically states, in part, that drain piping shall be installed at uniform slopes.

OK, thanks. I feel a little better about the smaller slope. What about the pipe thickness? SD-26 or 35?

SDR pipe is made to the "Size Dimension Ratio". Under SDR to determine the wall thickness the diameter of the pipe is divided by the guide number.

Example: for 4" SDR-35 pipe the wall thickness would be 4/35= 0.114" and 4" SDR-26 would be 4/26= 0.154".

By comparison, PVC schedule 40 pipe, which is made to the IPS (Iron Pipe Standard) the average wall thickness for a 4" pipe would be 0.237", which is more than twice the thickness of the SDR-35 pipe.

While code does permit the use of both PVC Sched. 40 and SDR pipe for the "house Sewer Line" in my humble opinion when you consider the cost of the pipe when compared to the cost of excavation and installation labor the minor amount saved by using SDR pipe is a false economy, especially if you live in a region subject to rocky soil or heavy tree roots. Personally, If it was my house I would insist upon using sched.40.

It should also be noted that code requires a "Main Cleanout" at teh point where the "house Sewer" meets the "house Main Drain". For structures that have a basement the main cleanout is generally placed inside the basement within 3' of the footer wall. For structures on slab the main cleanout is to be placed on the outside within 3' of the footer wall, and for structures built over a crawl space the cleanout may be placed at either of the above mentioned locations.

You are required an additional cleanout for every 80 linear feet of pipe and at any change of direct that is equal to or greater than 45deg.