Plumbing in the Home/sump drains to septic?


QUESTION: in my new home the previous occupants rigged a system where the sump pump drains into the septic system. wondering if this is a bad idea because every time we get lots of rain the whole house stinks up with sewer smell.  there's a small creek out back that it should probably be "piped out" to. what makes it more complicated is the washing machine is in the basement and they rigged that to drain into the sump so the sump takes the washing machine water into the septic.  If I piped the sump outside I would need to somehow get the washer pumped up and over to the septic.
any ideas?

ANSWER: Hi Mark,
A septic tank is a carefully designed biological system.  Putting anything other than normal wastewater into it can cause problems. This includes excessive groundwater. The discharge from a washing machine is actually considered "grey water" and many people actually create gray water capture systems to use for irrigation. It is, however okay to pipe it into the septic system.

Since you are experiencing sewer smells back into the house, the problem is not that they are using a sump pump to pump the washing machine effluent out to the septic tank but that the system is improperly installed and not correctly vented.

Any drainage system for wastewater requires proper venting. There are two reasons for this; 1. To pipe away the naturally occurring sewer gases,(methane) and 2. To break the vacuum within a closed system so that the pipes will actually drain. All plumbing vent terminations need to be routed up to at least a foot above the roof line. If this is not feasible or practical, a device called a "AAV" (air admittance valve) or mechanical vent can be used. These devices have a one-way diaphragm type valve that only allows air into the system but not out. If one of these is already installed on the system, it is malfunctioning and needs to be repaired or replaced.

On a side note, the wastewater from a washing machine is actually considered "gray water" is not generally considered to be toxic. As opposed to "Black water" such as the drainage from a toilet, which is very toxic, gray water is usually the discharge product from showers, hand sinks and washing machines. In many parts of the country, this water is actually captured in a dedicated system and used for irrigation of plants and lawns. You may want to do a little research on this subject. It might be the answer you're looking for.

CAUTION... Draining any household drainage system to a local creek is a very bad idea and probably a violation of local ordinances in addition to being environmentally unsound. Wastewater from a washing machine typically has a lot of phosphates from the detergent. Phosphates actually act as a fertilizer and can cause severe algae blooms and other environmental problems with both the water quality and with the wildlife that depend on this creek for a food and water source. Please don't do that.
Good Luck,

---------- FOLLOW-UP ----------

QUESTION: while that's A LOT of information, you didn't really answer my questions. maybe I didnt ask them clearly so lets try this.  I'll just ask the questions simply and individually.

1 - is it a bad idea to have my sump pump/ ground water constantly being dumped into my septic system?

2 of course I wouldnt have cloths washer water go into the creek! but is it ok to have the sump (ground water only) piped out to the creek?

3 since the washer needs to drain into the septic (obviously) do you have any ideas to pump it up and over to the septic system (since the washer itself is about 5-6 ft lower than the septic system piping in the house?


Hi Mark,
1. Yes, it's a bad idea to pump ground water into the septic.  It was designed to handle the drainage from the number of fixtures you have, not additional ground water.

2. Yes, piping naturally occurring ground water to the creek should not be a problem.

3. They make package systems for sewer ejection specifically designed for basement fixtures. Typically a holding tank that the fixture drains into and a pump with a 2" discharge line and check valve. You would only need to connect it to the main line going out to the septic. Inside or outside the foundation depends on the setup and access to piping that is available.

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Dana Bostick


Pretty much any residential plumbing questions. For "item specific" details such as a specific model of fixture, I will need to research and there may not be any useful information available. Note: I live and work in Southern California. We do not, as a rule, use hot water or steam heating systems, oil fired boilers or private water wells so my knowledge in those areas is pretty limited. There are others here on AllExerts that can probably answer those questions better.


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