Cal. Code Regs. tit. 25, § 2268 – Pipe Size.

(a) Each lot drain inlet shall be assigned a waste loading value of six (6) fixture units and each park drainage system shall be sized according to Table 2268-1 or as provided herein. Drainage laterals shall be not less than three (3) inches in diameter.
(b) A park drainage system in which the grade, slope, or sizing of drainage pipe does not meet the minimums specified in Tables 2268-1 or 2268-2 shall be designed by a registered engineer for a minimum velocity flow of two (2) feet per second.
(c) Park drainage systems installed without P-traps or vents may be sized for individually vented systems in accordance with Table 2268-1 for individually vented systems.
(d) A park drainage system which exceeds the fixture unit loading of Table 2268-1 shall be designed by a registered engineer.
Table 2268-1
Drainage Pipe Diameter and Number of Fixture Units on Drainage System
Maximum No.
Maximum No.
Terminal &
of Fixture Units
of Fixture Units
Relief Vent
Size of Drainage
Individually
Wet Vented
Wet Vented
Pipe (Inches)
Vented System
System
System (Inches)
3
35
14
2
4
180
35
3
5
356
180
4
6
600
356
4
Table 2268-2
Minimum Grade and Slope of Drainage Pipe
Slope
Slope
Pipe Size
per 100 ft.
Pipe Size
per 100 ft.
(inches)
(inches)
(inches)
(inches)
2
25
6
8
3
20
8
4
4
15
10
3 ½
5
11
12
3

Note: Authority cited: Section 18865, Health and Safety Code. Reference: Section 18873.1, Health and Safety Code.

1. New section filed 7-6-2004; operative 7-6-2004 pursuant to Government Code section 11343.4 (Register 2004, No. 28).