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Question DetailsAsked on 10/17/2017

If the septic tank inlet is 5" lower than outlet line but neither can be lowered or raised, what options are there?

Outlet cannot be lowered due to very little pitch to d. box and inlet line cannot be raised due to very little pitch from the foundation to the septic tank. Is this a big problem? What is recommended to fix the issue? Cost estimate?

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1 Answer


That certainly sounds like an invitation to plugging of the inlet line - though whether that will actually happen or not depends on a lot of factors, and may be as simple to solve as being sure to hold the flush handle down till the tank totally empties (if a standard sized tank) so you get about 4-5 gallons per flush rather than the 2-3 most modern flush hardware provides, to flush out solids better - this assuming your water costs arenot exhorbitant. And maybe having the line jetted every few years to clear any incipient buildups, as opposed to the more normal 10-20 year interval. You can do a lot of few hundred $ jettings over the years for the couple thousand range (or more) you are probably looking at for other possible corrective measures.

Of course, the primary thing to be sure of is that the solids level in the tank not come up to the inlet pipe level - meaning a deliberate schedule of checking the solids level and getting it pumped before that happens. After a while you will have a good feel for how many years your system can go between pumpings - but again you can do a fair number of extra pumpings at maybe $300-600 each commonly (though sometimes up to $1000 range) for the cost of reconstructing your system - especially considering most of the pumpings would have to be done anyway, so you might only be adding an "additional" pumping every 5-10 years on the average, in addition to the normal ones that would be needed. The "additional" frequency change would be small - say keeping the solids level 6-12 inches below normal on a probably 4-6 foot diameter tank might mean about 10-20% more pumpings over the long term - so averaging out over the long run, maybe around 450/year ballpark added average cost for the added pumpings. This presumes that the inlet will flow OK into liquid, just not into solids buildup, which would normally be the case. Course, if the line grade is so low that there is no inflow pressure at all, then existing into liquid could result in backup in the inlet pipe itself, which could block it pretty quickly. Normally not a big issue because if the sewage starts backing up in the stack that adds flushing power - but if you have a line which runs through the lowest level in the house with drains at that level wiothout a significant (foot or more say) drop into the stack, that can cause a problem.

Of course, how long you intend to stay in this home and how close to its service life the leach field is matters too - you would be more incllned to put more $ into a permanent fix or, if system is really getting old and clogging up, prehaps even a totally new septic systeminstallation [typically about a 25-50 year occurrence] if this is your "forever" home than if you expect to move in a few years.

What the situation in the house is matters too - if the leach field fills up (heavy rain, blockage, etc) is this going to cause a backup into household drains - if so, something that should definitely be remedied.

If it gets to be a real problem, than the solutions (short of a major septic system rebuild) would be:

1) put a septic tank lift pump in to pump the tank effluent to the distribution box - keeping the liquid level in the tank the recommended amount (typically 3-6 inches) below the inlet pipe level - though of course that makes your system highly power-dependent unless you make that the primary discharge but still keep the existing outlet pipe usable as a backup in case of pump/power failure.

2) look at regrading the sewer pipe from the house - not much you can do if a slab-on-grade house, but commonly the outdoor sewer line to the lowest level of the house can be raised somewhat - to give a higher level to the start of the horizontal run to the septic tank, thereby allowing raising the inlet pipe level too.

3) more extreme, but sometimes the outdoor line level is based on a basement bathroom or floor drain - if that is the case, commonly you can instead run the discharge to the outdoor line from the main floor sewer line (at approximately ground level) which might give enough elevation to redo the outside line to correct grade - then connect any basement drains through a sewage lift pump (grinder/lift pump if any kitchen or toilet down there) to lift the basement flow up to discharge into the ground level piping - abandoning the old lower elevation line. Of course, that makes the bottom level (basement) dependent on power for pumping out the sewage - and added maintenance cost for that sewage lift pump.

Of course, this sort of realignment also has to consider required pipe burial depth for protection against damage, and also frost depth. And of course realigning the sewer line means a new penetration to the septic tank at a higher level and capping off the existing inlet - which depending on tank design and materials may or may not be easy to do.

My recommendation - get a Civil Engineering firm that does septic system design and certifications to look at your specific situation and evaluate what can be done and provide a cost estimate for alternatives which might work in your case.

You could also have a Septic Tank contractor look at it - but their forte is not system design and they are not equipped or experienced in surveying the exact current elevations and such, so I recommend the Engineer route - probably about $500 for an evaluation and recommended design (which you will likely need engineer stamped drawings for any way to get a building permit for any changes to be made).

Bottom line - having lived in a house like this when I was a kid - very minimal inlet pipe slope and it came in about a foot below static water level, experiencing a blockage only every decade or so (which may or may not have anything to do with the low inlet pipe), personally I would not go all-out on a repair, at leaat not initially - you can always move to that as phase II if necessary.

I would go with scheduled jetting of the line and solids level checking in the tank for a while to see what happens. Of course, if a blockage could cause a backup into the house and drain overflows because you have drains below top of septic tank level, that picture changes dramatically compared to a house where the drain line in the house is above-ground level at the point where it exists the house - like suspended from crawlspace or basement subfloor joists then down into the ground at the foundation. Of course, that situation is also the cheapest to fix in terms of regrading the drain line from the house to the tank to raise the tank inlet - possibly with some insulation or added soil if needed to provide pipe cover depth.

Answered 2 years ago by LCD

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