This paper covers the use of storage tanks for rehabilitating hydraulically deficient sewer systems. The use of such detention tanks is considered to offer a cost effective means of upgrading sewer systems with hydraulic problems. The latest procedure for investigating both the hydraulic and structural problems of sewer systems is outlined and the use of detention tanks placed in context. Alternatives to traditional resewerage methods are described. Three principal reasons are identified for providing storage in sewer systems, and the requirements for good tank design are described. These are discussed under the headings of hydraulics, tank configuration and sedimentation.