Most septic tank problems show up as one of four things: a smell, a soggy patch in the garden, slow drains, or sewage backing up into a toilet or shower. Common causes include a full tank, a blocked pipe or a French drain that has stopped absorbing, but a symptom on its own isn't a diagnosis. Sewage coming back into the house is urgent.
What's going wrong, and what to do about it
The same sign can have more than one cause. Use this table to start the conversation with the operator, not to settle it.
| What you notice | Possible causes, not a diagnosis | What to do |
|---|---|---|
| Bad smell around the tank, drains or outside | Tank due for a pump-out, or a French drain struggling | Check when it was last pumped. If nobody knows when it was last pumped, arrange an inspection and ask whether pumping is needed |
| Soggy patch or standing water near the tank or drain | Tank overflowing, or the French drain can't absorb any more | Keep children, pets and vehicles off it. Ask for the tank and the drain to be looked at |
| Slow drains, toilets slow to flush | Full tank or a partly blocked pipe | Ask the operator to check the tank and the pipe. If it was pumped recently, the pipe or drain is worth a look |
| Sewage backing up into toilets, showers or drains | Tank full, or the outlet or French drain blocked | Stop using water and treat it as urgent (see below) |
| Backups or wet ground come back soon after a pump-out | A blocked outlet, a French drain not accepting liquid, or another fault | Don't just book another pump-out. Ask for the inlet, outlet and drain to be checked |
| Trouble started after strong chemicals went down the drain | The tank's working bacteria may have been killed off | Stop the chemicals and tell the operator what was used |
Two of these deserve a second look. First, a tank that refills after pumping is normal: a working septic tank sits full to its outlet level. What isn't normal is backups that keep coming, effluent surfacing or a level that sits abnormally high. Those need the inlet, outlet, tank and drain area assessed. Our French drains and soakaways guide explains more. Second, chemicals matter more than most people think: one Pretoria operator lists chemicals that "could have destroyed all the beneficial bacteria" as a cause of overflowing tanks.
What not to put in a septic tank
The US Environmental Protection Agency (EPA) says it plainly: "Your septic system is not a trash can." Only human waste and toilet paper should go in.
Keep these out:
- Wet wipes and paper towels
- Cooking fat, oil and grease
- Coffee grounds and cat litter
- Medicines
- Oil-based paint, solvents and large amounts of harsh cleaners
- Chemical drain openers. For a blocked drain, ask a plumber or the operator
Grease is the sneaky one. It goes down hot and liquid, then sets in the pipes and the tank.
Do Ridex, other additives or vinegar help?
This is one of the most searched septic questions, so here's what the evidence says, and what it doesn't.
Additives in general. Ridex is one of several products sold to "boost" a septic tank with added bacteria or enzymes. We don't sell, rate or recommend any product. The most useful independent guidance we found is the EPA's 2024 fact sheet on septic tank additives. It says their use "is not recommended for domestic wastewater treatment", because a working system already contains the bacteria, enzymes and other microorganisms it needs. It adds that some products may interfere with the breakdown of waste or contribute to clogging, and that independent research on many of them is limited.
Drain and line cleaners. The same fact sheet says products with strong acids or alkalis can harm the bacteria and damage pipes and tanks.
Vinegar. We couldn't find reliable guidance, South African or otherwise, that says vinegar helps or harms a septic tank. So we won't claim either. What the EPA does list, for every household, is regular inspection and pumping.
If a product is being sold to you as a fix for a smell or a slow drain, ask the operator first. The symptom may be a full tank or a dead French drain, and no bottle changes that.
When is a septic problem urgent?
Treat it as urgent when:
- Sewage is coming back into the house. An Eastern Cape plumber's guide calls sewage backing up into toilets or drains "an emergency", and it is.
- Sewage is pooling where people or animals walk. Children, dogs and horses don't read warning signs.
- The tank is overflowing at the cover.
What to do while you wait:
- Stop using water. Hold off on showers, the dishwasher and the washing machine. Every litre has to go somewhere.
- Keep people and pets away from wet areas.
- Leave the cover closed and don't lean in. A septic tank produces gases including hydrogen sulphide and methane, according to the EPA. Never enter a septic tank or try to rescue someone inside one. Gases and lack of oxygen can kill.
- Locate the access cover and clear loose items around it, and clear a path for the truck. Leave lifting the cover and opening the tank to the operator. One operator's access condition is the manhole within 30 metres of the truck.
Then call 060 086 9889 or send a request. A vetted local septic operator in your area calls you to confirm the price and a time.
Can I sort it out myself?
Small things, yes: stop the chemicals, fix a running toilet, keep the drain field clear. Emptying the tank, no.
In Tshwane, the Sanitation By-laws say anyone carting sewage must be authorised to do so, and must offload it only at a facility allowed to accept it. Waste removal services also need a licence under the National Environmental Management: Waste Act. That's a job for a properly set-up operator with a vacuum truck, not a borrowed pump.
Sources for the figures on this page
- "Bad smells around drains or outside"; "Overflow or soggy patches near the tank area"; "Slow drains or frequently clogged toilets" wolfplum.co.za
- "Sewage backing up into toilets or drains, this is an emergency" biggsplumbers.co.za
- Chemicals "could have destroyed all the beneficial bacteria"; blocked French drain outlet; manhole access within 30 m suckaseptic.co.za
- "Your septic system is not a trash can"; flush only human waste and toilet paper; keep out wipes, grease, coffee grounds, cat litter, paper towels, medications; no oil-based paints, solvents or large volumes of toxic cleaners; avoid chemical drain openers www.epa.gov
- Additives "not recommended for domestic wastewater treatment"; microorganisms already present; may interfere with breakdown, contribute to clogging; limited research; acid and alkali line cleaners harm bacteria and damage pipes and tanks; tanks produce hydrogen sulphide and methane; regular inspection and pumping www.epa.gov
- Sewage carriers must be authorised and offload only at an authorised facility (s11(2), s11(4)); waste removal needs a NEMWA licence and the City's authority (s7(9)) archive.opengazettes.org.za