waste pipe slope: how much is too much?

I am planning the installation of a waste pipe (either 3" or 4") over a distance of 46 feet. The drop in elevation over that distance is 30", which I calculate to be aprx .65 inches per foot (instead of the nominal .25 inches per foot). Is .65 inches per foot too much? I COULD excavate more at the high end, and come closer to the .25 inche per foot, but is it worth the extra effort? Also, does the pipe size make a difference?
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j probose wrote:

The only problem with too much slope is that velocity will be higher and solids *may* tend to settle out.
4" pipe will have lower velocity, so may help a bit. In the end, you probably won't have any problems with this run.
I would install cleanout TEE's brought up to the surface at each end.
Jim
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I've heard this all my life. Not wanting to start a war but can someone prove it is true?
I just don't buy it; for a couple of reasons. Sediment doesn't settle out in a flowing stream. It only settles in eddies or broad flat stretches with slow flow.
Even if it is true, the second flush liquid will push the first flush solids.
And the ultimate slope, a vertical drop, doesn't seem to be a clog problem due to settling.
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Vertical has gravity working for it along with no drag. A steeper than appropriate drop could certainly have issues with solids settling on it. The flow ends up being 'too quick' and moves over the solids instead of just pooling up slightly behind it and forcing it along. I think there's also the issue with how solids might build up over time. I'm sure there's a more scientific explanation out there.
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On Thu, 22 Dec 2005 23:05:26 -0500, "Bill Kearney"

I don't get it. Why wouldn't this be even worse with an average drop? The liquid would go slower but so would the solids.

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Bill Kearney wrote:

always proceed toward larger pipes.
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wrote:

Yes, that's too much. You should go for between 1/8" and 1/2" per foot, trying for as close to 1/4" per foot as you can get.
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go as far as possible with the standard slope (.125/.25" pf) and for whatever elevation is remaining, make a jog with a pair of 1/8 bends. do not use ells for this. you must be able to run a cable through it.
bill

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j probose wrote:

I have that much slope or a little more and have had no problems in the 12 years it has been installed. People will tell you that too much slope will leave solids behind, and it may for a short time. But when you use the bath tub, washer, or flush without solids, the solids will wash down to their intended location. Now if you had a run of a couple of hundred feet it may be a different story, but 46' should not give you a problem.
Bob S.
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