Plumbing Fundamentals

Plumbing is one of the core building trades. Every residential and commercial structure depends on properly installed water supply and drainage systems to deliver clean water and safely remove waste. As an apprentice plumber, you will learn to work with a range of piping materials, make reliable joints, lay out drain-waste-vent (DWV) systems that comply with the International Plumbing Code (IPC), and install fixtures that will serve building occupants for decades. This guide covers the materials, techniques, code principles, safety protocols, and real-world tips that working plumbers rely on every day.

Pipe Types and Materials

Different piping materials serve different purposes. Choosing the right material for the application is one of the first decisions on any plumbing job.

Copper

Copper has been the standard for water supply lines for decades. It resists corrosion, handles high temperatures, and has a long service life.

• Type M - Thin wall, identified by a red stripe. Used for most residential water supply. Nominal sizes 1/2" and 3/4" are the most common for branch lines.
• Type L - Medium wall, identified by a blue stripe. Required by many codes for underground supply, commercial buildings, and where local amendments demand it. More resistant to damage and corrosion.
• Type K - Thick wall, identified by a green stripe. Used for underground water service lines and municipal water mains.

Copper is available in rigid (hard-drawn) and flexible (soft) rolls. Soft copper is used where the pipe must follow curves, such as refrigerant lines and underground service connections.

PEX (Cross-Linked Polyethylene)

PEX has become the dominant water supply material in new residential construction due to its lower cost and faster installation.

• Color-coded: red for hot supply, blue for cold supply, white for either
• Available in 3/8", 1/2", 3/4", and 1" sizes for residential work
• Flexible enough to make sweeping turns without fittings, reducing potential leak points
• Cannot be used outdoors where exposed to UV light - UV breaks down the material
• Three connection methods:
  • Crimp rings - Copper or stainless steel rings compressed with a crimp tool. Most common method. Use a go/no-go gauge to verify every crimp.
  • Clamp rings (Cinch) - Stainless steel rings tightened with a cinch tool. Easier in tight spaces because the tool approaches from one side.
  • Push-fit (SharkBite style) - Push-on connections that grip the pipe. Convenient for repairs but more expensive per fitting and not accepted by all inspectors for concealed locations.

Tip from the field: Always use a pipe support every 32 inches on horizontal PEX runs and at every change of direction. PEX expands and contracts more than copper, so leave a slight droop between supports rather than pulling the pipe tight.

PVC (Polyvinyl Chloride)

PVC is the standard material for drain, waste, and vent lines in residential construction.

• Schedule 40 is standard for DWV applications - white or light gray
• Joined with a two-step process: purple primer followed by PVC solvent cement
• Available in sizes from 1-1/2" (lavatory drains) through 4" (building drains and sewers) and larger
• Not rated for hot water supply (maximum service temperature around 140 degrees F)
• Must be supported every 4 feet on horizontal runs per IPC Table 308.5

ABS (Acrylonitrile Butadiene Styrene)

• Black plastic pipe used for DWV in many western US jurisdictions
• Joined with ABS solvent cement only - no primer required
• Some jurisdictions do not allow ABS, so check your local code before using it
• Cannot be directly cemented to PVC - a transition fitting or mechanical coupling is required

CPVC (Chlorinated PVC)

• Rated for hot and cold water supply up to 200 degrees F
• Joined with CPVC-specific primer and cement - never use PVC cement on CPVC
• Light yellow or cream colored
• Less common in new construction since PEX became widespread, but still found in repairs and some commercial work

Cast Iron

• Found in older buildings and still specified in commercial work for its sound-dampening properties
• Modern installations use no-hub cast iron joined with stainless steel band clamps and neoprene gaskets
• Heavier and more difficult to work with than plastic, but significantly reduces water noise through drain pipes

Tools Every Apprentice Needs

A plumbing apprentice should have these tools on the first day:

Cutting and Preparation:

• Tubing cutter (for copper, sized for 1/4" through 1-1/8")
• PVC ratchet cutter or hacksaw
• Reamer (inner/outer for removing burrs from cut pipe)
• Deburring tool
• Emery cloth or sand cloth (for cleaning copper before soldering)

Assembly and Fitting:

• Crimp tool and go/no-go gauge (for PEX)
• Propane torch with self-igniting tip (for soldering copper)
• Lead-free solder and water-soluble flux
• Channel-lock pliers (10" and 12")
• Basin wrench (for faucet mounting nuts in tight spaces)
• Pipe wrenches (14" and 18" for steel and iron pipe)
• Teflon tape (yellow for gas, white for water) and pipe dope

Layout and Measurement:

• Tape measure (25-foot minimum)
• Torpedo level (9")
• 2-foot and 4-foot levels
• Marker and scratch awl

Safety:

• Safety glasses (always wear when cutting, soldering, or working overhead)
• Work gloves (for handling rough pipe and fittings)
• Fire extinguisher (required when soldering near combustibles)
• Fire-resistant cloth (for soldering near framing)

Soldering Copper Pipe

Soldering (sweating) copper joints is a fundamental plumbing skill. A properly sweated joint is stronger than the pipe itself and will last the life of the building.

Step-by-Step Procedure

1. Cut the pipe square using a tubing cutter. Rotate the cutter around the pipe, tightening slightly with each revolution. Do not over-tighten - this creates a ridge inside the pipe that restricts flow.

2. Ream the inside edge with the triangular reamer on the back of the tubing cutter or a dedicated reaming tool. This removes the burr created by cutting.

3. Clean the pipe end with emery cloth or a wire fitting brush. Clean 1 inch of the pipe end until the copper is bright and shiny. Do not touch the cleaned surface with your fingers - oils from skin prevent solder from flowing.

4. Clean the inside of the fitting with a fitting brush sized for the pipe. The inside of the fitting cup must be uniformly bright.

5. Apply flux to both the pipe end and the inside of the fitting using a flux brush. Use a thin, even coat - excess flux causes corrosion inside the joint over time. Use only water-soluble flux for potable water systems.

6. Assemble the joint and twist slightly to spread the flux. Make sure the pipe is fully seated in the fitting cup.

7. Heat the fitting, not the pipe. Apply the torch flame to the body of the fitting, moving the flame around the joint to heat it evenly. The fitting has more mass and needs more heat.

8. Touch solder to the joint on the opposite side from the flame. When the fitting is hot enough, capillary action will draw the solder into the joint. You should see a ring of solder appear around the entire circumference. For 1/2" pipe, about 1/2" to 3/4" of solder wire is sufficient.

9. Wipe the joint with a damp (not wet) rag while still hot. This creates a clean, professional appearance and removes excess flux.

Common Soldering Mistakes

• Not cleaning thoroughly enough - This is the number one cause of failed solder joints. If the solder balls up instead of flowing into the joint, the surfaces were not clean enough.
• Overheating - Burns off the flux and oxidizes the copper, preventing solder flow. The joint should be hot enough for solder to flow within 5-10 seconds of applying heat.
• Water in the line - Even a small amount of water inside the pipe will prevent a proper solder joint. Use bread (yes, regular white bread wadded into a ball) to dam small amounts of residual water. It dissolves and flushes out when the water is turned on.
• Not supporting the joint - Copper softens when heated. If the pipe is not supported, it can sag and the fitting can shift before the solder solidifies.

Code requirement: All solder and flux used on potable water systems must be lead-free per the Safe Drinking Water Act. Lead-free solder contains 95-97% tin with small amounts of copper, silver, or antimony.

Drain, Waste, and Vent (DWV) Systems

The DWV system is the other half of every plumbing installation. It removes wastewater by gravity and uses venting to maintain atmospheric pressure so traps function correctly.

Key Principles

• Gravity flow - All drain and waste pipes must slope downward toward the building sewer. The standard slope is 1/4 inch per foot for pipes 3" and smaller, and 1/8 inch per foot for pipes 4" and larger (IPC Section 704.1).
• Traps - Every fixture drain connects to a trap (typically a P-trap). The trap holds 2 to 4 inches of water that creates a seal against sewer gases. If a trap loses its water seal, sewer gas enters the living space.
• Venting - Vent pipes extend from the drainage system up through the roof. They serve two purposes: allowing air into the system so water flows freely (preventing siphoning of traps), and allowing sewer gases to escape above the roofline.

DWV Pipe Sizing

Per the IPC, pipe sizing is based on drainage fixture units (DFUs):

• Lavatory: 1 DFU (1-1/4" or 1-1/2" drain)
• Bathtub/shower: 2 DFU (1-1/2" or 2" drain)
• Kitchen sink: 2 DFU (1-1/2" drain)
• Toilet (water closet): 3 DFU for 1.6 GPF models (3" minimum drain, 4" for building drain)
• Washing machine: 2 DFU (2" drain)
• Floor drain: 2 DFU (2" minimum)

The building drain and building sewer are typically 4" for residential and must handle the total DFU count for the building.

Fitting Selection for DWV

DWV fittings are specifically designed for gravity drainage. Using pressure fittings on drain lines is a code violation and causes blockages.

• Sanitary tee - Used for horizontal-to-vertical connections. The sweep directs flow in the proper direction. Never use a sanitary tee on its back (horizontal to horizontal) - this creates a crossflow that causes blockages.
• Wye fitting - The preferred fitting for horizontal branch connections. The 45-degree entry angle promotes smooth flow.
• Combo (wye + 1/8 bend) - Combines a wye with a 45-degree elbow. This is the correct fitting for connecting a horizontal branch to a horizontal drain.
• Long-sweep elbow (1/4 bend) - A gradual 90-degree turn. Required on horizontal drain lines. Short-radius elbows are only allowed on vent lines or where the drain turns from horizontal to vertical.
• Cleanout fittings - Access points for clearing blockages. IPC requires a cleanout at the base of every stack, at every change of direction greater than 45 degrees, and every 100 feet on horizontal drains.

Vent Types

• Individual vent - Serves a single fixture. Connects to the fixture drain and rises to the vent stack or through the roof independently.
• Common vent - Serves two fixtures connected at the same level on opposite sides of a vertical drain.
• Wet vent - A vent that also serves as a drain for another fixture. IPC Section 912 allows wet venting for bathroom groups in residential work. For example, the lavatory drain can serve as the wet vent for the toilet and tub.
• Air admittance valve (AAV) - A mechanical one-way valve that allows air into the drain system when negative pressure occurs. Accepted by the IPC (Section 917) in most applications except as a replacement for the main building vent through the roof.

Tip from the field: When roughing in DWV, always install your vent connections above the flood-level rim of the highest fixture served. This prevents wastewater from backing up into the vent. The flood-level rim is the top edge where water would overflow (the top of the sink basin, for example).

Fixture Rough-In Dimensions

Getting rough-in dimensions right prevents costly rework after the walls are closed. These are standard dimensions - always verify with the fixture manufacturer's specifications:

• Toilet - 12" from finished wall to center of closet flange (most common; 10" and 14" rough-ins also exist). Closet flange sits on top of finished floor with the flange ring 1/4" above the floor surface.
• Lavatory - Supply stubs at 4" to each side of center, 20-22" above finished floor. Drain at center, 18-20" above finished floor.
• Bathtub - Drain rough-in per manufacturer spec (typically 14-15" from back wall to center of drain). Valve body centered at 28" above subfloor. Tub spout at 4" above tub rim.
• Kitchen sink - Supply stubs at 4" to each side of center, 20-22" above finished floor. Drain at center, 16-18" above finished floor.
• Washing machine - Supply valves (hot and cold) at 42" above finished floor. Drain standpipe 2" minimum diameter, between 18" and 30" above the trap weir.

Water Supply System Design

Pipe Sizing for Supply

Water supply piping must be sized to deliver adequate flow and pressure to all fixtures. Key factors:

• Street pressure - Typically 40-80 PSI. Measure with a pressure gauge on the hose bib closest to the meter.
• Pressure loss - Occurs through pipe friction, fittings, elevation change (0.43 PSI per foot of height), and the water meter.
• Flow demand - Based on fixture unit count per IPC Table 604.3. A typical 2.5 bathroom home needs a 1" main supply line, with 3/4" branches to bathroom groups and 1/2" branches to individual fixtures.
• Velocity - IPC limits velocity to 8 feet per second to prevent water hammer and pipe noise. Size up if flow calculations put you near this limit.

Water Hammer Prevention

Water hammer is the loud banging that occurs when a fast-closing valve (like a solenoid valve on a washing machine or dishwasher) stops water flow suddenly. The shock wave can damage pipe joints and fittings over time.

• Water hammer arrestors - Small devices with a sealed air chamber that absorbs the shock. Required by the IPC at washing machine valves and dishwasher supply. Install vertically with the chamber pointing up.
• Securing pipes - Properly supported pipes are less susceptible to water hammer damage. Use pipe clamps, hangers, or straps per code spacing requirements.

Testing Your Work

Every plumbing installation must be tested before it is concealed or put into service.

DWV Testing

• Air test - Plug all openings and pressurize the DWV system to 5 PSI using an air compressor. The system must hold pressure for 15 minutes with no drop. This is the most common test for new construction.
• Water test - Fill the system with water to the highest vent opening. The system must hold the water level for 15 minutes with no drop. Used less often because of the weight and mess involved.

Supply System Testing

• Pressure test - Pressurize the supply system to the working pressure or as required by the local inspector (typically 50-80 PSI for residential). Hold for a minimum of 15 minutes. Walk every joint and connection looking for leaks.

What Inspectors Look For

• Proper slope on all drain lines (1/4" per foot minimum for pipes 3" and smaller)
• Correct pipe sizes per the code
• Traps on every fixture drain
• Vent connections at or above the flood-level rim
• Cleanouts at required locations
• Proper pipe support spacing
• Correct materials and fittings for the application
• No cross-connections between potable and non-potable systems
• Test results (they may witness the test or verify your test gauge)

Safety Protocols

Plumbing work involves several hazards. Follow these safety practices:

• Soldering and brazing - Keep a fire extinguisher within reach. Use a fire-resistant cloth behind joints when soldering near wood framing. Check the area 30 minutes after soldering to make sure nothing is smoldering.
• Cutting and drilling - Wear safety glasses. When drilling through framing, check for electrical wires and other utilities first. Use nail plates on studs where pipes pass through to protect them from drywall screws.
• Trenching - Any trench deeper than 5 feet requires shoring or sloping per OSHA. Even shallow trenches can collapse - never work in an unsupported trench.
• Sewer and drain work - Sewer gas contains hydrogen sulfide, which is toxic. Work in ventilated areas. Never enter a sewer manhole without confined space entry procedures.
• Chemical safety - PVC primer and cement are flammable and produce toxic vapors. Work in ventilated areas. Keep containers closed when not in use.
• Lifting - Cast iron pipe and full water heaters are heavy. Use proper lifting technique and get help for heavy loads.

Common Mistakes Apprentices Make

1. Not reaming pipe after cutting - The burr inside the pipe restricts flow and catches debris, leading to blockages.
2. Using the wrong fittings on DWV - Pressure fittings (like standard tees) do not have the proper sweep for drain lines and violate code.
3. Insufficient slope on drain lines - "Close enough" is not good enough. Use a torpedo level with a slope indicator or calculate the drop over the run and measure it.
4. Forgetting cleanouts - Inspectors will catch missing cleanouts every time. Plan them into your layout from the start.
5. Cross-threading pipe fittings - Start threaded connections by hand before using a wrench. If it does not turn easily by hand for the first few turns, back it off and try again.
6. Not testing before closing walls - This is the most expensive mistake. A leak behind drywall costs far more to fix than a leak you catch during testing.
7. Mixing pipe materials incorrectly - PVC cement on ABS, or CPVC cement on PVC, creates joints that look solid but fail under pressure. Always match the cement to the pipe material.

Tips from Experienced Plumbers

• "Measure twice, cut once" applies to plumbing more than any other trade. A pipe cut 1/4" too short means starting over.
• Dry-fit your DWV assemblies before cementing. Lay everything out, check your slopes, and verify your dimensions. Once PVC cement sets, the joint is permanent.
• Keep your fittings organized. A 5-gallon bucket with compartments for different sizes saves enormous time on the job.
• Take photos of every wall before it is closed. When someone needs to locate a pipe later, your photos are worth their weight in gold.
• Learn to read blueprints. The plumbing plan tells you exactly where every fixture, pipe run, and connection goes. Apprentices who can read plans advance faster than those who cannot.

Key Takeaways

• Match pipe material to the application - copper or PEX for supply, PVC or ABS for DWV
• Clean and flux copper joints thoroughly before soldering, and always use lead-free solder on potable water
• Maintain proper slope on all drain lines: 1/4" per foot for 3" and smaller, 1/8" per foot for 4" and larger
• Every fixture drain needs a trap and a vent connection to function properly
• Test all work before closing walls - air test DWV to 5 PSI, pressure test supply to working pressure
• Follow IPC requirements for pipe sizing, fixture rough-in dimensions, and cleanout locations