Here is an example of how you would use a trap adapter in a dual kitchen sink installation
TRAP ADAPTERS FOR USE IN RESIDENTIAL SINK DRAINS
Trap Adapters are divided into two main categories, male trap adapters and female trap adapters, the difference is explained below.
This is commonly referred to as a female trap adapter, but is also known as a Hub trap adapter because it fits over the pipe. These come in a variety of sizes from 1 1/4" to 4" for every day residential plumbing. Additional sizes are available for commercial use. Trap Adapters also come in a variety of shapes and lengths, depending on the manufacturer or the application.
This is a male or Spigot type residential trap adapter. It is very similar to the female trap adapter except that you insert it into a fitting instead or pushing it over a pipe or other fitting like you would with a female type trap adapter. Both come in a variety of materials, the most common being PVC and ABS. Commercial applications often use copper or brass trap adapters.
Unless you work in a plumbing store, you will have no idea of how many people get this wrong. To most people this is a "thing-a-majigy" that you use somewhere, in plumbing, so you had better get one. The majority of do it yourselfers don't have a clue what they are called or how to use them. They come in a variety of sizes, material, shapes and uses. Unless you know the type and size that you need, you will without a doubt get the wrong one. That means that you will have to make another trip to the store and waste more time, instead of getting the job done right the first time. In this article I will try to explain "trap adapter" in detail and clear up any of the confusion that exists around them. Let's get started.
Simply put, trap adapters are used to connect a kitchen or bathroom sink to the drain pipes. They have many other purposes as well, but I think if you understand how they can be used for a kitchen, laundry tub or a bathroom sink, you will begin to see how they can be easily adapted to solve many other household plumbing problems.
This is a 1 ½" ABS Female Trap Adapter that would normally be used to install a kitchen sink, laundry sink or bar sink. All kitchen sinks, laundry or utility sinks as well as most bar sinks, are all designed for a 1 ½" drain tail piece. (Bathroom sinks use a 1 ¼" tail piece). It fits over a 1 ½" ABS pipe and slides over a 1 ½" tail piece.
This is a standard 1 ½" male ABS trap adapter, that is designed to fit inside a fitting, like a "P" trap or pipe coupler. Apart from the fact that it fits inside as opposed to outside the pipe, it is identical in all respects to a regular (female) trap adapter.
The difference between an ABS or PVC trap adapter designed for a kitchen or bathroom sink and one design to fit over a copper pipe is that the copper pipe adapter has a larger inside diameter, so they won't work on, a kitchen or bathroom sink. Kitchen sink tail pieces are 1 ½" and bathroom sink tail pieces are 1 ¼" in diameter; always!
Copper pipe trap adapters, like regular plumbing trap adapters come in both the male and female version. The male version (shown above) is very useful if space is limited and you require a shorter connection. They can reduce the overall length of a drain connection by ½".
Copper Pipe Trap Adapter
NOTE: Trap adapters made for copper pipe, state right on them "COPPER PIPE ADAPTER" as well as the size of pipe intended for.
Another distinquising factor, about copper pipe adapters, is that they often have two "wings", one on the right and one on the left, of the compression cap "screw on ring".