Plumbing Cheat Sheet 2026

The 30 highest-yield Plumbing facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What is the minimum burial depth for a residential water service line in a climate with a 36-inch frost depth? → At or below the local frost line (36 inches)
2. What type of wax ring alternative provides a better seal for uneven floors when installing a toilet? → Double-stacked wax ring or foam gasket seal
3. Which regulation requires plumbers working on lead service lines to follow specific work practice standards to protect workers and residents? → EPA Lead and Copper Rule and OSHA Lead Standard
4. What is the purpose of the overflow tube in a toilet tank? → To prevent the tank from overflowing by routing excess water to the bowl
5. What does a 'rough inspection' verify in plumbing construction? → That all rough-in pipe installations are correct before walls are closed
6. What is the purpose of a pressure reducing valve (PRV) in a residential plumbing system? → To reduce high incoming water pressure to a safe level
7. What is the purpose of a lead-free requirement in US plumbing codes? → To protect potable water from lead contamination in fittings and solder
8. What is the purpose of an air admittance valve (AAV)? → To allow air into the drain system without a traditional vent pipe
9. What is the purpose of a dielectric union? → To prevent galvanic corrosion between dissimilar metals
10. Which pipe is rated for both hot and cold water supply lines? → CPVC
11. What is a 'stack vent' in a plumbing system? → The extension of a soil or waste stack above the highest fixture connection
12. What tool is used to make flared connections on soft copper or aluminum tubing? → Flaring tool
13. Which pipe material is best suited for underground sewer lines due to its chemical resistance? → Schedule 40 PVC
14. Which appliance connection typically REQUIRES a flexible gas connector rather than rigid pipe? → Gas range/stove
15. What is the recommended setting for a residential water heater thermostat to balance energy efficiency and safety? → 120°F
16. What personal protective equipment (PPE) is most important when soldering copper pipe? → Safety glasses and heat-resistant gloves
17. What fitting is typically installed at each gas appliance to allow individual shutoff without interrupting the entire system? → Appliance shutoff valve (gas cock)
18. What type of trap is prohibited in most US plumbing codes? → S-trap
19. Which type of fitting is required when changing direction from horizontal to vertical in a drain system? → Long-sweep 90-degree elbow
20. What is cross-connection in a plumbing system? → A physical link between potable water and a non-potable source
21. What is the minimum clearance required in front of a toilet per the IPC? → 21 inches
22. What is the purpose of a garbage disposal air gap on a dishwasher drain connection? → To prevent dishwasher drain water from backflowing into the dishwasher
23. Where must a manual gas shutoff valve be installed for a new gas appliance? → Within 6 feet of the appliance in the same room, in an accessible location
24. What is the term for the main vertical drain pipe that carries waste from upper floors to the building drain? → Soil stack
25. What is the safe, approved method for detecting a gas leak at a fitting or connection? → Apply soapy water and watch for bubbles
26. How is copper pipe typically joined in a residential water supply system? → Sweat (solder) fitting or press fitting
27. What is the purpose of a press fitting system (like ProPress) in copper plumbing? → To create permanent crimped connections without soldering or open flame
28. Which gas has a specific gravity GREATER than air, causing it to sink and accumulate in low areas? → Propane (LP gas)
29. What is the minimum required separation between a gas meter and electrical service equipment? → 3 feet
30. What prevents sewer gases from entering a building through a floor drain that is rarely used? → A trap primer or trap seal preservative