Household hygiene is not a hot topic on a farm, but your wastewater system needs to work non-stop for you, your family and your farm workers to function as unaffected, normal human beings.

The wastewater your home produces is referred to as ‘effluent’ and consists of blackwater (toilet waste) and greywater (shower, sink and laundry waste). Effluent flows directly from your household plumbing into a watertight, underground septic tank.

Roto Tanks manufactures a sturdy two compartment septic tank which offers many extra benefits. The septic tank operates by digesting solids and settling sludge to the bottom and allowing grease to float to the top in the first compartment. Between these two scum layers is a zone of clarified liquid effluent which is internally piped to the second compartment of the septic tank for additional settling. As incoming sewage from the house fills the first compartment, clarified liquids are forced to leave the second chamber of the septic tank and flow out to the leach field or leach pit.

 The typical leach field is a series of chambers or rock filled trenches where effluent is further treated as it slowly percolates through the soil. A leach pit is a deeper, larger hole filled with rock for disposing of wastewater in a smaller footprint. A leach pit is not as effective as a larger leach field. Where sewage percolates slowly over a larger area, leach pits are an alternative for smaller properties only where high seasonal ground water is not present. Greywater from washing machines, sinks and showers contains soaps designed to kill bacteria (clean and disinfect things) and thus discourage optimal septic tank function.

You want to encourage helpful good bacteria (digesting anaerobic cultures) to grow in your septic tank and organically treat the waste, not kill helpful bacteria with detergent laden greywater. It is best practice to divert household greywater to a separate leaching area.

 Never use bleach, drain cleaner, or harsh soaps with a septic system. Bleach and detergents kill the helpful bacteria that thrive in a healthy septic tank to optimally process toilet waste. Lack of proper septic tank bacteria will cause your leach field to fail from excessive bio-mat accumulation.  Never use any of those septic tank or leach field chemical additives and miracle enzyme cures that supposedly break down fats and solids in the septic tank. These additives simply allow smaller particulates to pass through the septic tank where they re-unite in the leach field forming a dense biomat. At best, they will do no harm to your septic system or the environment, just waste your money. The FDA (U.S. Food and Drug Administration) does not approve of any of them – none of these septic cleaning and/or maintenance products have been proven effective in the long run.

The deciding factor should be to ask yourself if you would like to see these additives find their way into your well water and thus your digestive system. A properly designed septic tank (large enough with two compartments) is going to operate just fine without those overhyped additives.

Plastic is best

Roto Tanks offers septic system site plan design tips and tricks for installing your own septic tank and leach field. Plus, practical advice on how to repair a septic system leach field. They also offer consultation on best-practice installation procedures, system design improvements, and potential operational issues in the future.  Farmers have to take note that Roto Tanks is a plastic moulder and not an engineering firm. They do not provide any soil testing, on-site services, ‘stamped’ engineered plans, or ‘advanced treatment’ septic systems.

Clients are highly encouraged though, to submit their site plan for free review after purchasing one of Roto Tanks’ septic systems. Unlike concrete, plastic tanks are not affected by high ground water and saturated soils, which will eventually erode concrete, forcing replacement. Plastic has many advantages over concrete in addition to durability in wet locations. It boasts consistent quality, and ten-way inlet and outlet ports. Polyethylene tanks will never crack or leak and they are easily moved around by two people, saving money, the need for heavy machinery and making it easier to build on difficult locations.

Best practice to install a 5 000 litre two-compartment septic tank

Even if you are allowed to install a smaller tank, a larger tank will save money in the long run. Larger tanks need to be pumped less often and there is a much smaller chance of eventual bio-mat formation in the leach field. Larger tanks retain effluent for a longer time, allowing solids to settle on the bottom and grease to float to the top. Plus, a larger tank will allow expansion of your house later. Slower percolation rates due to poorly draining soil with clay, bedrock, high ground water, proximity to a creek, or other complications require larger leach fields. A general rule-of-thumb when estimating the leach field percolation rate is 35 litre per square metre of leach field is enough for 3,85 tons in normal soils that percolate relatively well.

 Your septic system site plan is typically drawn right on top of your property survey, showing the septic system ‘setbacks’, with the tank 1,5 to 3 metres from the house, the leach field at least 6 metres from the house, at least 30 metres away from wells and streams, 7,5 metres away from dry gulches, and 3 metres away from property lines, or whatever the local regulatory officials require. The home’s sewer line drain pipe needs to slope 2 cm for every m downhill to the inlet side of the septic tank and the outlet pipe needs to flow downhill at least 1 cm for every metre downhill to the leach field, where the septic tank effluent enters a manifold or distribution (D) box. Beyond the manifold or D box, it is excavated perfectly level at a depth of at least 18 cm below the grade of the manifold pipes or D box and covered with at least 30 cm of soil atop the trench. Trenches can be deeper if the site dictates, but rarely more than 1 m below the finish grade.

 Check both compartments yearly and pump the waste out before enough solids accumulate in the first compartment, which might spill over into the second compartment. Depending upon the tank design, this is usually about 40 cm maximum depth of sediment. Wrap a piece of disposable paper towel around the end of a disposable stick to check the solids level on the bottom of your septic tank.

Pumping a properly sized septic tank

A healthy, properly sized septic tank might never need to be pumped, but not pumping when needed will result in grease and solids getting out to the leach field. Particulates, grease and solids create a bio-mat in the leach field percolation area, eventually caus ing it to fail and to be cleaned and built again. The normal cycle for pumping a septic tank is every four to seven years (less often in warmer areas and/or lower usages).

Without water inside, an empty septic tank is under extreme stress, resisting the weight of backfill around it. This is especially true when soil is wet and when tanks are not properly bedded in plenty of gravel. Stress is critical when sewage pumpers park too close to the tank, so always keep their truck at least 6 m away. With enough stress, an empty concrete and fiberglass tank will crack,start leaking and eventually have to be replaced.

 Every septic system has two distinct components. A septic tank to catch solids and a leach field to dispose of liquid. Leach pits are large gravel filled holes and leach pits take advantage of the surface area around the sides of the hole to dispose of large amounts of water in the right soil types.

Leach fields are trenches (or rectangular beds) dug in the yard and filled with 25 to 50 cm of gravel. A 10 cm diameter perforated pipe is placed inside and along the trench. The pipe-in-gravel leach line is covered with geotextile fabric (landscaping weed barrier) and then backfilled with a 30 to 60 cm of native soil atop. Gravity sends the effluent to the leach field with at least a 1 cm per metre drop. The wastewater is then dispersed into the soil evenly with the leach field perforated pipe being at the same level.

 Septic tank installation is relatively straight-forward, but even seasoned professionals can get mired in how they have always done it to realise there are better ways to approach any project. Roto Tanks is here to help their clients during every step of the way, doing their best to ensure you don’t make that one critical mistake, like not using risers, or not venting your leach field properly. Clients are highly encouraged to submit their site plan for a free review after purchasing one of their septic systems.  

Lack of ventilation at the ends (at least) of each leach field lateral line (finger) is the most common cause of leach field failure – no fresh air in the pipes. Septic systems contains hazardous human waste and must be approached with proper safety equipment and plenty of caution. Wear disposable protective clothes with full head/mouth covering, face shield and/or goggles, protected sleeves and gloves.

 Oxygen is especially important to leach field health and a drywell with surface vent at the end of every lateral line is an instant fix for that, while greatly increasing the capacity and drying out the lateral lines at the same time. Taking the load off your failing leach field is crucial to any repair. An excellent long-term fix is to add one (or more) of the Roto Tanks drywell kits.  The first step in fixing failures is to examine why it failed in the first place. The most common reasons for leach field failure are a single compartment septic tank, an under-sized leach field and lack of leach field ventilation.

E-mail sales@rototankzambia.co.zm or call 096-056-7058 or 097-192-6953 for more information, or visit their website at www.rototanks.com.