PVC waste pipes began to replace metal waste pipes in the home starting in the 1970s. PVC is easier to work with as it does not require pipe-fitting or soldering. Where most PVC waste pipe joints are glued together permanently, some connections may require a different type of joint. A slip joint allows for a quicker connection of two different types of waste pipe. You can even use a slip joint to connect metal waste pipe systems with a PVC sink drain.
Permanent Drain Pipes
Part of the waste pipe system of your home is permanently installed. This is done during the plumbing rough-in process during building construction. Waste pipes are normally embedded into walls, floors or ceilings and are not visible in the normal living areas of the home. Building plans call for the proper waste pipe locations, but you cannot install the actual sink drain until after the basin has been installed, which is usually much later in the building construction. Every sink is different and the contractor doing the plumbing rough-in may have no idea what type of sink will be installed later. This means there has to be some way of tying the sink drain yet to be installed with the permanent waste pipe system.
Waste Pipe Materials
Many homes built before the 1970s used a metal waste pipe system -- usually copper, cast iron or brass. Metal may seem sturdy, but over time it may corrode and leak. Polyvinyl chloride is a type of plastic that became the material of choice for most plumbers to construct waste pipes from in later homes. PVC pipes do not corrode and are less expensive than the metal counterparts. PVC drain pipes can be tied into metal waste pipe systems in older homes.
Whether you want to connect a PVC sink drain to a metal or PVC waste pipe system, you can use a PVC slip joint for this procedure. The permanent waste pipe system usually protrudes the wall or floor a few inches. A slip joint adapter, which looks like large plastic retaining nut, slides onto the end of the drain pipe from the sink. You insert the drain pipe into the permanent waste pipe. The slip joint connection allows back-and-forth movement of the drain pipe so you can get the correct adjustment, then you tighten the adapter to seal the connection.
Some plumbers may not use PVC slip joints, but will glue the drain pipe to the waste pipe. This may be a more permanent connection, but you will need to cut the pieces if you need to make repairs to the plumbing. A slip joint allows you to disconnect and reconnect the connection just in a few minutes.