Common Septic Systems: How They Work and Typical Issues

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Septic systems are important, and just because they're underground and can be mostly forgotten about doesn't mean we don't need to take care of them once in a while. If neglected entirely, they can be very difficult to ignore once something does go wrong. Domestic treatment plants and septic tanks of all kinds need regular maintenance.

Before you can maintain your septic system, you'll need to know how it works! Here are the fundamentals for the most common types of systems, and some of the issues which can arise.

Basic (gravity) septic systems

If a building has a gravity septic system to treat waste water, then all the main drainage pipes in it are connected to one main exit pipe. This exit pipe feeds waste water to the septic tank, usually located underground and not far from the building. Anything put down the drain goes to the septic tank.

Here, the waste water separates in to solid and liquid. Solids fall to the bottom of the tank to form the sludge layer, effluent sits in the middle, and any liquids lighter than water (such as oils) sit at the top forming the scum layer.

An outlet pipe makes sure that only the effluent flows out of the tank and into the soil in the drainage field. Typically, the outlet is connected to a distribution box, which ensures that the effluent is equally dispersed into the pipes in the drainage field. Finally, holes in the drainage field pipes allow the safe effluent to flow into the soil. These pipes are surrounded by a layer of gravel, allowing a consistent flow of effluent. 

The most common problem for a gravity septic system is sludge build up. If the sludge layer is left for long enough to reach the outlet pipe level, your septic system will become clogged. The solution is simple in theory — clean the tank often enough. About once a year is standard. It is highly recommended that you call in a professional for the job. 

The distribution box will also need to be cleaned out if it becomes clogged, which should be easy enough, provided you know where it is.

Lastly, the drainage field needs to be left alone. Don't do anything (drive over it, plant anything but grass on it, build on it) which will compact or affect the soil there in any way. You could crush or break the pipes, and this will be a costly problem to resolve. 

Most of these issues, whilst not avoidable forever, can be ameliorated if you don't put the wrong stuff down the drains. Simply try not to put solids, oils or strong chemicals down there if at all possible. 

Pressurised systems

These are similar to gravity systems but use a pump to move the effluent to the drainage field. Pressure systems are used where the drainage field must be located in higher ground than the septic tank or where a very consistent flow of effluent is required. If the soil in the drainage field will only take a certain amount of effluent per day, for instance, the pump can ensure that the correct amount is dispersed, allowing the soil to dry out between doses. The pump in located in its own tank, which is connected, in series, after the septic tank. Sensors in the tank tell the pump when to be "on" and "off" and when the water level is dangerously low or high.

Pressurised systems require electronic pumps. Electronics and waste water make for a dangerous mix. A pressurised system will have an alarm to tell you if there is something wrong. If the alarm goes off, call a professional. Don't attempt to fix these dangerous parts yourself.