Size of pipe to the Septic Tank?

I have a 3" line from under the house. The guy I spoke with that does Septic Systems says 4" no less.
My run is about 85' from my house to the Septic Tank. I have the 1/4" per foot Fall from the House to the tank.
Should I upsize the pipe to 4" or just keep the 3"
I don't want my liquids to run from the Solid, so I though that the 3" would be better?
Thanks!
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[is this for an existing or new system? is there a problem now?] talk to your neighbors if they have similar lots and hills of pitch. and the pump out sewage company. then your local plumbing permit office and health department. plan piping in advance for a future municipal hookup. always better to design properly when it comes to plumbing. basics at: http://en.wikipedia.org/wiki/Septic_tank http://people.howstuffworks.com/sewer.htm
Scott Townsend wrote:

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Its a new house and new System. Well for the most part anyway... new 2nd Dwelling, new lines, new tank, etc. Old tank will drain into new tank, which will pump up to the field.
So my concern is more of the liquid running away from the solids. I've heard that the 4" gives you the better flow, easier to clean, etc, but the 3" makes it so your liquid level is higher to carry away the solids.
So with an 85' run @ 1/4" per foot drop, should I upsize from the house's 3" to 4" to the tank, or just leave it at 3"?
Thanks

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I'd make it 4".
http://www.eng-tips.com/viewthread.cfm?qid 2208&page=1 http://www.howstuffworks.com/sewer2.htm
http://muextension.missouri.edu/explore/envqual/eq0401.htm In all septic tanks, the inlet and outlet pipes should be at least 4-inch diameter Schedule 40 PVC, cast-iron or other approved pipe and be protected by baffles or sanitary tees made of acid-resistant concrete, acid-resistant fiberglass or plastic.
http://www.deq.state.or.us/WQ/wqrules/Step3.pdf#search=%22septic%20system%20pipe%20size%22 ?? Sewers shall be minimum 4" diameter, installed with tracer tape or toning wire.
?? Sewers shall be designed to flow half full, based on 1 gpm per dwelling and Manning's n = 0.013. Minimal
velocities are acceptable. However, low-velocity and flooded sections may require sulfide controls.
?? Subject to a 4" minimum diameter, inverted siphons shall be designed to flow at a velocity of 0.5 feet per second
or greater, based on a Hazen-Williams coefficient of 100.
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Thanks for the info!!!
Scott<
wrote in message

http://www.deq.state.or.us/WQ/wqrules/Step3.pdf#search=%22septic%20system%20pipe%20size%22
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On Fri, 25 Aug 2006 05:20:18 GMT, "Scott Townsend"

3 inch is fine as long as you restrict the size of your turds when you take a shit. Stitching part of your asshole shut will help. Be sure to use hi-test nylon fishing line for the stitches so they last for years.
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