Manholes Specifications and sizes: Mid-State Concrete Products Inc. manufactures all manholes in accordance with the requirements of ASTM C-478 specifications. The concrete compressive strength is 4000-PSI minimum. All circular manholes are wet cast in standard diameters of 36", 48", 60" and 72" with a variety of heights to meet your projects needs. The manholes have a 6" wall thickness accepts for 72" which is 7" walls. Uses: The precast manhole bases are a monolithic pour to assure a watertight base section. They can be used for sanitary sewer and storm drain systems, pump stations, and wet wells. Invert channels as well as inlet and outlet holes are cast to your specified details. Flexible watertight pipe- to- manhole boot connectors are also available for most pipe sizes.  Precast concrete manholes have many different uses. We can cast them with any of the following, a specified protective lining, custom holes, or top sections to accept covers, grates, and doors. Benefits of Precast Concrete: Precast manhole structures provide the owner and installer cost savings, assured quality, speed in construction time, as well as reduction of environmental concerns on the job.