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GregWCIL 06-26-2008 10:03 PM

How long a run to septic tank?
We are getting ready to dig the hole for a new house. It will be on a long, gently sloping field. Today, the plumber suggested we might be able to do away with a sewer pump for the basement bathroom by running the sewer line 2 to 300 feet down the slope from the house to a septic tank.

I own a tiling machine that will dig deep enough to do the job--and very accurately using laser control to maintain 1/10th ft. drop per 100 ft. run.

My question is if that long a run to the septic tank is ok?


concretemasonry 06-26-2008 10:23 PM

I am sure you can dig accurately.

Check any local requirements for slope and length if you ever expect to sell the property. Also look at surrounding area requirements since they can change. Make sure it is inspected by someone!

I had an system installed and received a certificate from the county (complete with seal) that described the approved system (pipe sizes, distribution box, tank capacity, drain tile length, etc.) that I had installed. Because it was lakeshore, the certificate or documentation was worth more than the cost of the system about 10 years earlier.

I did not need a "real" building permit in an unincorporated area , but need a thorough electrical inspection and certification, but no requirement for sanitary. Fortunately, I had a contractor that did things right, so I got the unexpected "gift" certificate from the county.

GregWCIL 06-26-2008 11:07 PM

Sometimes I wonder who to trust-advice wise.

For example, the plumber said the sewer drain should have little or no fall-I asked if that meant .1 foot per 100 ft. of run (the minimum we install field drainage tile.) He said that was perfect.

Now, I check the Illinois code and it says 1/8 in. minimum per foot (that works out to 1 ft. per hundred or 1 percent--huge difference.

Maybe I need a different plumber.

Alan 06-26-2008 11:23 PM

1/4 per foot inside building and 1/8 outside is pretty standard

Mike Swearingen 06-27-2008 03:30 AM

Do you or do you not have to have a local Health Department septic system permit and inspection and a plumbing inspection?
In most places, the Health Department tests the soil and custom designs the septic system for each property based on the soil type and proposed usage level.
At 1/8" per linear foot outside from the home to a septic tank 300' away, it would be a 37.5" lower difference at the line into the septic tank than the house basement septic line exit elevation (1/4" per foot slope inside basement).
Does your property slope that much? The tank should be shallower than that as it should be pumped out at least every five years.
I would install line cleanouts at regular intervals along that slope, also.
Check with someone besides that plumber IMHO.

majakdragon 06-27-2008 10:32 AM

I would do some serious checking on the long distance of the tank from the house. In Florida and Arkansas, the tank is required to be within 10' of the house. Pitch on the piping is 1/8" per foot outside the foundation and 1/4" inside of it. This is due to larger piping being used for the main drainlines.

GregWCIL 06-27-2008 03:10 PM

I have to get a local permit for the septic tank. I will check on codes. Sounds like the 1/8th in./ft. is fairly standard.

I will check on the length of run also, but I'm not too worried about it. Our trencher can maintain +/- 1/4 in. accuracy.

I'm actually surprised they specify that steep a grade. I've seen tile water running at one tenth that grade with pretty good velocity.

Thanks again for the help,

mstplumber 06-27-2008 08:37 PM

Usually the Health Department makes the rules concerning septic tank location and design. If you show them where you would like to install the tank, they should be able to give you an answer. The soil will need to be tested where you plan to install the drainfield.

1 % is very standard across most codes for 4" pipe. A full size (4" in this case) clean out is required at specified intervals, probably every 100' but check your local code. Mike is right, septic tanks need to be fairly shallow, 1' to 2' deep is perfect.

GregWCIL 06-28-2008 03:04 PM

OK--here's the answer
Thanks for all the suggestions.

I talked to a well respected local septic service man. I am taking his advice since he sees all the problems caused by improper installs. Here's what he says:

In this era of low-volume flush toilets, keep the septic tank as close as possible. Lift pumps are very reliable, so use one so the septic line leaves the basement wall about 18 in. below final grade.

Our county health dept. has you do your own perk test. I plan to test a location for the lateral field at least 100 ft. away to avoid conflicts with future landscaping.

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