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
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.
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
And the ultimate slope, a vertical drop, doesn't seem to be a clog
problem due to settling.
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.
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.
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.
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