What is the difference between a soakaway and a drainage field?

A soakaway is a pit or crate-based structure used for the attenuation and gradual release of rainwater (surface water) into the ground. Soakaways were historically used to receive septic tank effluent, but this has not been legal since 2007 and should not be confused with a drainage field.

A drainage field (also called an infiltration system) is the legal method of discharging treated effluent from a septic tank or sewage treatment plant to the ground. It consists of parallel, gravel-filled trenches fitted with perforated pipes, through which the effluent slowly percolates into the surrounding soil. Drainage fields must be designed and installed in accordance with British Standard BS 6297 and the relevant Building Regulations.