Understanding the intricacies of the drain, waste and vent (DWV) system is fundamental for anyone working in the plumbing industry. 

By diving deep into the world of DWV system pipe and joining methods, we aim to provide comprehensive insights and practical knowledge. This will enhance your expertise and empower you to deliver exceptional service and solutions to your plumbing contractor customers. 

DWV systems are essential for a building’s plumbing, removing wastewater and ensuring airflow for water movement to septic or sewer systems. They include drains for gravity-led water removal, waste sections for used water from toilets and sinks, and vents to prevent vacuum in piping and sewer gas entry into living spaces.

Plumbing vents, or vent stacks, are crucial in the DWV system. They allow sewer gases to escape into the air, preventing dangerous buildup inside the home. They also let air into the plumbing system to balance the pressure, ensuring a smooth flow of water and waste through the pipes. 

Air must follow water down the drain to prevent a vacuum in the pipe and ensure smooth drainage. A vent stack, extending from the interior drainage pipe to above the roof, balances pipe pressure and prevents traps from losing their seal. This keeps sewer gases out of the building. 

For years, plumbers have navigated the nuances of various pipe materials when constructing DWV systems. From PVC and ABS to cast iron and copper, each material has its strengths and applications. 

Let’s take a deep dive into these piping materials and their associated joining methods and solutions. 

Plastic Pipe Options

• PVC (polyvinyl chloride). PVC pipe is a top choice in the plumbing sector for its affordability, light weight and resistance to chemicals and bacteria. It is particularly suitable for drain and vent lines due to smooth interiors, preventing scaling and facilitating waste removal. 

In contrast to older piping materials, PVC stands out for its durability and minimal failure rate. This low-carbon plastic piping does not corrode or degrade over time, as supported by studies highlighting its reliability compared with other piping options.

• ABS (acrylonitrile butadiene styrene). While sharing characteristics with PVC, ABS pipe is notably better suited for colder climates due to its superior performance in extreme temperatures. This makes it a more prevalent choice in colder areas. Containing a chemical known as bisphenol A (BPA), ABS pipe gains increased durability and hardness. 

ABS pipe, known for its black color, is less flexible than PVC but offers superior strength and cold resistance. It comes in 10- and 20-foot lengths in the United States, providing a cost-effective option without sacrificing quality. Both ABS and PVC serve similar functions and have similar installation processes.

ABS pipe is lighter due to its foam core, making it cost-effective and robust, suitable for many plumbing applications. Both ABS and PVC pipe can transmit noise, which may be a concern in noise-sensitive environments. In such cases, cast-iron pipe, known for its sound-dampening properties, might be preferred.

• CPVC (chlorinated polyvinyl chloride). CPVC pipe, less common in residential plumbing than PVC or ABS, excels in managing chemical waste thanks to its chlorine content. This modification boosts its temperature resistance and resilience against chemical solvents.

It is highly valued in laboratories, pharmaceuticals, chemical processing and other applications for its exceptional chemical resistance. Its ability to withstand corrosive substances, outperforming other plastic piping types, makes it an ideal choice for chemical applications and factory drainage systems handling chemical waste.

CPVC systems are highly durable and reliable for transporting aggressive chemical waste, preventing leaks that could occur with less-resistant materials. This makes CPVC a crucial, albeit less common, component in DWV piping, often discussed among professionals in chemical waste management for its ability to withstand caustic materials.

PVC, ABS and CPVC Pipe Joining 

For a secure, lasting connection in PVC, ABS, and CPVC pipe joining, primer and solvent cement are crucial to prevent plumbing failures. Solvent cementing chemically welds two pipe surfaces together that, once cured, create an airtight seal.

• Primer application. To select the right primer, first identify the material of the pipe being joined. For example, you will want to use a PVC-specific primer for PVC pipe. Apply the primer before cementing to clean the surface and soften the pipe with solvents, making it porous for a strong solvent weld.

Primer can be applied only to PVC and CPVC applications, not ABS pipe. Some primers, such as the Hercules Purple Primer, can be used for both PVC and CPVC. Local codes may require a purple primer to identify the proper application more easily. 

Oatey’s Industrial Grade Clear Primer is a more aggressive primer for commercial and large-diameter thermoplastic piping systems. It is appropriate for solvent-welding PVC and CPVC pipe and fittings and contains a clear finish.

The maximum application temperature for primer is 110 F. When applying it, plumbers should use an aggressive application to ensure that solvents are worked into the surface. Remember that the purpose of primer is to break down surface tension.

The primer should be applied to the fitting using an applicator. Once applied, the applicator should be redipped to apply to the pipe. ASTM standards require that the applicator be redipped one more time and applied again to the fitting itself. 

The cement should be applied while the primer is still wet (within five minutes). 

• Solvent cement application. Here again, to select the appropriate solvent cement, identify the piping material being fused to select the corresponding cement. For example, the Hercules ABS Medium Body Black Cement or Oatey Special Medium Milky Clear ABS Cement should be used only on schedules and classes of ABS pipe and fittings. Both are ideal for nonpressure applications.

The same concept applies to PVC cement. The Oatey PVC Medium Bodied Fast Set Clear Cement can be used on all schedules and classes of PVC pipe and fittings, particularly for the DWV system, pressure pipe up to 6”, potable water and electrical applications. The Hot Medium Blue Lava PVC Cement is formulated for wet conditions, quick pressurization and fast installation for DWV repair, irrigation, and pool and spa applications. 

For CPVC applications, products such as the Hercules CPVC Medium Bodies Fast Set Orange Cement are intended for CPVC Schedule 40 and 80 pipe and fittings for potable water and waste vent pipe applications. FlowGuard High Contrast 1-Step Medium Green CPVC Cement contains a vivid green color, indicating a properly solvent-welded connection.

• Transition couplings. Solvent welding is commonly used for joining PVC, ABS and CPVC, but transition or rubber couplings with steel jackets are alternatives, especially useful for connecting different materials: cast iron to PVC, PVC to cast iron or copper to ABS. These methods help adapt to varying wall thicknesses and ensure secure connections in DWV systems.

Cast Iron and Copper

Cast iron is a highly durable material used in plumbing for its ability to withstand high temperatures and pressures, making it suitable for industrial applications. Despite its heavy weight and the challenges in transportation and installation, it supports nearly 5,000 pounds per linear foot and offers fireproof qualities and low sound transmission. 

However, it is prone to corrosion from strong acids and deterioration from hydrogen sulfide gas. While still produced for its enduring qualities, cast iron’s significant weight can lead to sinking and cracking if not properly supported. Repairing and working with cast iron is also more challenging than working with materials such as PVC. 

However, cast iron’s fire resistance and sound-dampening capabilities continue to make it a valuable option for commercial and industrial plumbing systems.

DWV copper offers a corrosion-resistant, lightweight and flexible alternative, ideal for water lines but less commonly used in DWV systems than PVC or ABS. While its upfront cost is higher, copper’s malleability and easy joining process make it a favored choice for residential water supply lines. 

It’s worth noting that DWV copper — distinct from other copper piping due to its thinner walls and larger diameter — is designed for low-pressure systems and is typically found in older constructions. DWV copper pipe is identifiable by its yellow markings, with a wall thickness of .040 for a 1 1/4-inch pipe. 

For most situations, the industry is moving toward replacing copper DWV with materials such as PVC or cast iron, depending on the context. 

Cast Iron and DWV Copper Joining Methods

Historically, cast-iron piping used a hub and spigot with lead seals. Modern systems prefer no-hub designs using rubber couplings for easier installation and reduced noise, earning it the nickname “the quiet pipe.” 

Copper DWV pipe can be joined through soldering or special mechanical couplings. Although rarely used in DWV applications, these couplings may be beneficial in certain environments where soldering is not ideal.

Soldering creates a solid mechanical bond by melting solder into the joint, which is crucial for airtight and watertight connections in plumbing to withstand high pressure and temperature. 

Solder, an alloy used in various applications, is traditionally made from lead. Due to health concerns, lead solder is now avoided in potable water systems but was once preferred in DWV applications for its low melting point, ease of use and reliable sealing. While lead solder is still used in some nonpotable applications, alternatives are often recommended and required by current building codes.

Flux is an essential wetting agent that, once heated, will help direct the solder to flow into the fitting cup. Using a thin acid brush or flux brush, apply a light coating to the end of the pipe and the inside of the fitting. Then, immediately join the two together and wipe off the excess.

DWV systems ensure homes are safe, functional and comfortable. As a plumbing wholesaler, your knowledge and representation of these systems and products not only boosts your business but also ensures long-lasting peace of mind for plumbers and homeowners. In a field where accuracy and trust are crucial, take pride in your role as an essential advisor for plumbers, keeping homes safe and water flowing. 

Remember, it’s more than selling products; it’s about being a dependable guide for every plumbing need. 

Sean Comerford is the technical applications manager at Oatey Co. He is a third-generation tradesman with nearly 20 years of plumbing experience, including serving as the lead plumber for commercial/residential new construction, service and fire protection jobs. He holds an Ohio Fire Protection License for Sprinkler and Standpipe.