Regarding the water flow, it is worth noticing the drainage water should move from a cleaner area towards less clean one. Moreover, drain covers should be made of stainless steel and have a slope between 1.5 and 2.0%. A greater gradient is likely to cause bodily injuries to waist muscles and bones. Also, it is suggested to conjunct two faces with a chamfer, such as between floor and wall and between permanent fixtures. To reduce the treatment cost of a cesspool and to prevent blockages in the pipe, one should connect open drains and drain ditches to a grease trap before releasing liquid waste to the cesspool.
reference: Good Manufacturing Practice