Septic Tank Failure: Signs of Failing

Septic tank failure is very rare; it can become full and need to be pumped; it can be damaged due to shifting ground and corrosion of the concrete; and, they can even collapse. However, they’re not usually thought of as “failing” as much as being damaged, so the term may actually refer to the more common situation of a drain field failure. This post is about tank issues. If you’re unsure what part of the system is failing, please visit this post on overall system failure.




Many people think of the tank when they think about the system; however, the drain field is more prone to failing and more expensive to fix. Visit field failure for more info.

The most common source of problems is lack of pumping on a regular basis. The tank is basically just a large storage container that receives all waste from a home. Its main purpose is to provide a place for scum (fat, oil, grease, floating solids) and sludge (heavier solids) to separate from the water. As separation occurs, the scum forms a layer on the surface of the water, the sludge sinks and forms a layer at the bottom, and effluent (water that free of scum and sludge) stays in the middle.

They need to be pumped regularly because over time the sludge layer rises decreasing the volume inside. As the volume goes down, the waste has less time to separate into scum, sludge, and effluent; if the waste has too little time, then particles of scum and sludge will flow out of the tank potentially causing big problems in the drain field.

Causes of a Tank Failure:

  • Damage to tees/baffles: The outlet tee/baffle is a pipe that goes under the effluent surface so that as the water level rises, effluent but not scum can exit. The inlet tee has the same shape and mainly provides a buffer to keep waste and water from flowing too quickly into the tank and disrupting the settling process. Both tees can break off, but are easily fixed. It’s important to have your tank pumped regularly because the technician can usually tell if there’s a problem. The tees are easy to fix, but they can lead to the more expensive problem of drain field failure.
  • Damage to inlet and outlet pipe junctions: The tank is heavy and prone to settling in the ground, which can lead to snapping the pipe from the house and the pip out to the drain field. These are both minor repairs but will probably require a contractor with a backhoe to dig up the problem.
  • Damage to risers: In a concrete tank, the risers form a junction with the body. Since it’s hard to form good joints between concrete and due to the shifting ground, these joints can break; however, these breaks might cause leaks but won’t usually cause failure.
  • Damage to bacterial ecosystem: Fortunately, as sludge builds up inside, bacteria are constantly breaking it down so that we don’t have to pump nearly as often as we would otherwise, but putting harsh cleaners or drain openers down the drain can kill these bacteria and cause sludge to quickly rise. Additives like CCLS septic cleaner can replenish our tank’s ecosystem with specially-grown, helpful bacteria.

A failing tank doesn’t usually seem like a possibility because they are usually concrete or heavy plastic-type material and seem indestructible; however, they have an estimated lifespan just like every other system in the home.

  • Concrete, the most common type, can develop leaks do to the shifting ground around them. In fact, leaks are very common in the joint between the risers and the body because it’s hard to get a water-tight seal in concrete joints. Since most concrete units are precast and transported to a site, there can be leaks from the beginning. These leaks, however, don’t usually cause septic tank failure and can be fixed relatively inexpensively.
  • Fiberglass tanks are used sometimes do to their light weight and easier transport; however, they’re more prone to breaking than concrete tanks and are more difficult to fix.
  • Old Redwood tanks are prone to failure when the top and sides collapse. In fact, if you hear about a one caving in, it was probably one of these older units. They’re are illegal in most areas; however, many are still in operation.

Some Degree of Failure is Common
Septic System Failure Rates by State

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