The International Plumbing Code is making its way across the United States. It’s easy to tell based on the telephone calls I have been receiving. All are related to one subject — combination drain (waste) and vent systems.
If you review this section in the IPC, you will find it is the most liberal venting method of any plumbing code. Having worked with the committee that wrote this section, I can tell you it means what it says and is as liberal as it appears. The basic premise of a combination drain and vent system is to oversize the drain and forget about the vent. Well, almost forget about the vent.