Trap Talk
100: What is the purpose of a trap in a plumbing system?
Answer: To prevent sewer gases and vermin from entering the building.
100: What is the main function of a vent in a plumbing system?
Answer: To equalize pressure and protect trap seals.
100: What chapter defines the roles of the AHJ and installer?
Answer: Chapter 1 – Administration
100: What’s the minimum clearance in front of a toilet?
Answer: 24 inches.
100: What is the main purpose of a grease interceptor?
Answer: To separate and retain fats, oils, and grease before they enter the drainage system.
200: What is the required water seal depth for a trap?
Answer: Between 2 and 4 inches.
200: What’s the minimum required distance between a trap and its vent?
Answer: At least 2 times the pipe diameter.
200: What type of approval must all materials and devices have before use?
Answer: Approval by the Authority Having Jurisdiction (AHJ).
200: Which fixtures require an air gap in their waste connections?
Answer: Dishwashers, water softeners, and commercial food equipment.
200: What’s the difference between hydromechanical and gravity interceptors?
Answer: Hydromechanical uses flow control and baffles; gravity uses retention time and is usually outside.
300: Name two types of traps that are prohibited by the UPC.
Answer: S-traps and crown-vented traps.
300: Name three types of venting systems.
Answer: Individual vent, common vent, and circuit vent.
300: Explain the difference between building drain and building sewer.
Answer: Building drain is inside and extends to 2 feet beyond the structure; building sewer connects to the public sewer.
300: Name two approved materials for plumbing fixtures.
Answer: Vitreous china and cast iron.
300: Name two places where a sand interceptor is commonly used.
Answer: Car washes and garages.
400: Why is a double trap not allowed?
Answer: It can become air-bound, leading to drainage issues and possible trap siphonage.
400: What is a crown vent, and why is it not allowed?
Answer: A vent installed too close to the trap weir; it's prone to clogging and ineffective venting.
400: What chapter outlines general installation regulations?
Answer: Chapter 3 – General Regulations.
400: What determines the number of water closets in a public restroom?
Answer: Occupant load and use classification.
400: When is an oil and flammable liquid interceptor required?
Answer: In repair garages, factories, and gas stations with oily or flammable waste.
500: Explain how trap seal loss can occur and how it's prevented.
Answer: Loss occurs from evaporation, siphonage, or backpressure; it's prevented through venting and trap seal primers.
500: Describe how improper venting can affect trap performance.
Answer: It can cause siphonage or backpressure, leading to trap seal loss and allowing sewer gas into the building.
500: When can a plumbing code requirement be waived?
Answer: When an alternate method is approved by the AHJ.
500: Explain the installation rules for indirect waste receptors.
Answer: Must be readily accessible, trapped, and with an air gap or air break connection.
500: What are the performance requirements for FOG disposal systems?
Answer: Must limit effluent to no more than 100 mg/L (5.84 grains/gal) of FOG.