Ventilation, relief well, and emergency overflow

When it rains, the air in the sewer must make way for water. This means that the sewer system must have vent points. New homes usually have a downpipe for this purpose. Older homes do not have this pipe. In practice, this means that the air escapes from the sewer system via the downpipe. If there is no downpipe and the downpipe is disconnected from the sewer system, the air will find another way to escape. This often results in gurgling toilets and sinks.

You can prevent this by installing an alternative vent pipe. It is also useful to install a relief pit in the neighbourhood the older rainwater drainage system. You must ensure that the rainwater can still drain away when the infiltration facility is completely full during extremely heavy rainfall. We call this the emergency overflow.

Description of how venting, relief pit, and emergency overflow work

• 
  Rainwater (A) from the gutter flows through the downspout either above ground or underground to the infiltration facility.
• If wastewater or rainwater cannot drain away quickly enough due to a blockage, the water can drain away into the garden via a relief well or a scrub well (B).
• If the infiltration facility is completely full and the water cannot flow to a lower point on the surface, the rainwater (C) can drain away via the emergency overflow (relief well or scrub well) through the sewer system (C).
• The air (D) from the sewer system can now escape through a second pipe on the wall that is connected to the sewer system.