The requirements for fuel gas piping are located in either the plumbing code, the mechanical code, or the fuel gas code. The ICC decided to locate the complete fuel gas piping requirements in the International Mechanical Code (IMC).

The IPC includes sizing tables for piping systems based on various rainfall rates. The tables are established on sizing the storm drain for the maximum open channel flow conditions. These are the flow rates that prevent any pressure from being developed

The combination drain and vent system is based on the same premise as the circuit-vented system. Most plumbing codes place arbitrary restrictions on combination drain (waste) and vent systems because the systems appear too good to be true.

Sanitary drainage systems must have fittings that provide a smooth pattern of flow to reduce the likelihood of a stoppage. To avoid confusion, the IPC identifies the acceptable drainage fittings in Table 706.3.