Drain Pipe Setup

• Your tub not only has a main drain opening, but also an overflow drain opening to keep water from spilling up over the top of the tub. Both of the drain openings connect to drain pipes. The overflow tube runs down the backside of the tub while the waste pipe runs under the tub's bottom. Both drain pipes connect with a tee. The third tee connection feeds into the main drain pipe under the tub.
  
  

Pop-Up Stoppers

• When you actuate the built-in stopper for your tub, you press a lever mounted on the overflow drain's cover. With pop-up stopper mechanisms, the lever connects to a linkage on the other side of the overflow drain cover. This linkage feeds down the overflow tube and has a large spring on the end. The spring presses on an arm that feeds down the waste drain pipe under the bottom of the tub. This arm connects to the bottom of the pop-up stopper. A pop-up stopper completely seals the waste pipe from the water, keeping all of the water in the tub until you open the stopper.
  
  

Brass Plunger Stoppers

• Other built-in stoppers use a brass plunger to keep the water in the bathtub. You still actuate the stopper using a lever on the overflow drain's cover, and a linkage attaches to the backside of the cover. On the other end of the linkage sits a brass plunger. The movement of the linkage changes the position of the plunger. When the plunger sits low, it covers the waste pipe's connection to the pipe tee, stopping the water from draining out of the tub.
  
  

Water Draining

• When you close the tub's drain using a brass plunger stopper, some of the water will go into the waste drain pipe that sits under the bottom of the tub. Tubs without a stopper in the bottom of the tub have no way of blocking the water from entering the pipe, but the plunger will keep the water from flowing further. Once you push down on the lever on the overflow drain's cover, the plunger lifts up and the water begins to flow out of the waste drain pipe and into the sanitary tee before making its way down the main drain pipe. Since the pipe doesn't slope, some of the water stays in the horizontal drain pipe even after the rest of the water washes down the sanitary tee and into the main drainpipe. The leftover water evaporates out of the pipe over time.