PLumbing Question: Slope of main drain to septic tank

[boakley]

Hello... A question about the slope of the main drain from my cottage to my septic tank (new construction)

Here are the facts:
- I have a cottage that is 4' above the ground, built post on pad.
- septic tank about 25' from where majority of water/toilet drains in the cottage will be.
- first 15 - 20 feet will be under the cottage in heated crawl space then last 5 - 10' will not be under the cottage.
- mostly 3 season use but would like to build for 4 season use.
- tank feeds a field pressure dosing


Any experts who can advise on slope of the main drain or other pearls of advice?

Originally I was advised straight 4' drop from toilet / drains / shower almost to ground level than 3% grade rest of the way.


I would have thought a straight 4'/25' (rise / run) would have been the way to go.

[Tothebar]

What is the size of your building drain 3'' or 4'' ?

[BVERFEVER]

The plumbers I deal with say 1/4" per ft/
I install about 50 tanks per year and have seen many variables, but the straight shot is the best I have seen.
Is your tank a 2' burial or deeper?
You don't want the liquid to out run the solids so to much angle is not good either.

[quadrunner]

I'm a licensed plumber and you are aloud a 2% grade what I do to maintain proper flow I always go 1/4" per foot so on 25' you would have a 6-1/4" drop. But that is just a minimum you can go more. But if you go to much of a slope the liquids will flow to quickly and the solids will be left behind. And your main drain must be 4" from your main stack to your septic tank.

[boakley]

Originally Posted by BVERFEVER

The plumbers I deal with say 1/4" per ft/
I install about 50 tanks per year and have seen many variables, but the straight shot is the best I have seen.
Is your tank a 2' burial or deeper?
You don't want the liquid to out run the solids so to much angle is not good either.

thanks all... tank is 2' burial. Would like to go deep burial but my backhoe not big enough to do it so 2' is what i will have to live with.

Cheers

concensus seems like 1/4" / foot or so.

[boakley]

Originally Posted by rancher350

What is the size of your building drain 3'' or 4'' ?

I was planning 4" but always open to recommendations.

[Tothebar]

Originally Posted by boakley

I was planning 4" but always open to recommendations.

It has to be 4'' and 1/4'' per foot to meet code. I just thought you wanted to fix piping that was there before and didnt read it properly.

[Sasquatch]

A little trick if you want to go deeper. Dig yourself a "bench" to park your hoe on(one foot, two, three, it really is up to you) and that will give you more digging depth. When you're done installing the tank just backfill the bench and voilla, deeper tank.

[KodiJay]

1/8" per foot on 4" pipe is minimum code in manitoba. 3" pipe and under must be minimum 1/4" per foot.