Will A Septic Tank Smell After Being Emptied

A septic tank is an underground wastewater treatment system commonly used in rural areas where there is no access to a centralised sewer system. It is designed to collect, treat and dispose of domestic wastewater from households and businesses. When a septic tank is full, it must be emptied by a registered waste carrier to ensure proper operation and prevent potential environmental issues.

When a septic tank is emptied, the removal of the accumulated solids and liquids should eliminate any unpleasant odours associated with the system. However, several factors can contribute to a septic tank continuing to emit smells even after a professional service.

1. Residual Sludge or Scum One possible reason for a septic tank smelling after being emptied is the presence of residual sludge. Although the tank has been pumped out, small amounts of sludge can remain stuck to the walls or the base of the tank. These residual substances can continue to produce odours until they are fully broken down or flushed through.

2. Blocked Vent Pipes A common UK-specific issue is a blocked vent pipe (or “stink pipe”). These pipes are designed to allow gases to escape safely above the roofline. If the vent is blocked by debris or a bird’s nest, the gases are forced back down into the house or out of the tank manhole, leading to a persistent smell even after emptying.

3. Structural Damage or Faulty Seals If the tank has cracks, leaks or a poorly fitting manhole cover, it will not effectively contain wastewater gases. This results in odours escaping from the tank area. Additionally, if the baffles inside the tank are damaged, the “crust” cannot form properly, leading to increased smells.

4. Clogged Soakaway (Drain Field) The soakaway is responsible for the final treatment and disposal of the effluent into the soil. If the soakaway is “blinded” or clogged, the liquid cannot disperse, causing it to back up toward the tank. This stagnation creates foul smells that can linger long after the main tank has been emptied.

5. Dried Out U-Bends (Traps) Sometimes the smell isn’t from the tank at all. If a guest bathroom or a sink hasn’t been used for a while, the water in the “U-bend” can evaporate, allowing septic gases to travel from the pipes directly into the home.

While a septic tank should not smell after being emptied, lingering odours usually indicate an underlying mechanical or structural issue. Taking proactive measures, such as checking your vent pipes and ensuring your soakaway is healthy, will help maintain an odour-free system.