Changing the drain fitting on a bathtub may become necessary at one time or another. The old drain may rust out, discolor or leak with time and use. The process for replacing a tub drain described here is for a garden tub in a mobile home. In mobile home plumbing, there are often differences in bathtub drains, because these tubs do not always have an overflow tube. In this type, the tub drain may be just a seal and nut that you tighten onto the tub itself. In a standard site-built home, by comparison, the drain assembly is usually a threaded insert onto which a mounting nut is screwed from below.
Removing the old tub drain is the first step in changing a tub drain. You will have to look under the tub to determine how to do this. In some tubs, the drain fitting is removed from the top of the tub, while in others there is a retaining nut that will have to be removed from underneath. The directions that follow are for the type that is unscrewed from the top.
- If there are crosshairs in the tub drain, then you can use tub drain wrench (sometimes called a Dumbell wrench) to unscrew the drain fitting counterclockwise. Since most tub drains have been in the tub for a long time, the chance of getting the drain out in one piece can be slim. If the crosshairs break off, you will have to get the drain out using another means.
If the crosshairs on the drain break cut the fitting with a mini hacksaw or hacksaw blade. Cut down the threads and through the rim, but not deep enough to go into the tub itself. Then, make a second cut about a 1/2" away from the first cut. With a flat screwdriver, you can lever the cut segment out. Once the cut section is removed, use the flat screwdriver to pry up one of the edges of the drain fitting and unscrew it in the direction you would normally. The fitting should come out with a little work.
- Next, prepare the new drain fitting and the drain pipes for installation. Beneath the tub, you will find a trap secured by a nut. Unscrew the trap and move the drain pipes out of the way to make room for the installation of the new tub drain.
- Roll out an even bead of plumber’s putty and position it around the new drain fitting, then push it into the drain opening in the tub. The rest of the tub drain installation is done from under tub.
- From under the tub, push the rubber seal then the retaining nut onto the tailpiece of the drain fitting. Screw the nut on until the fitting is tight. If the drain fitting spins instead of tightening, you may need a second set of hands to help hold it in place from above the tub while you tighten it from underneath. The tub drain wrench can hold the drain fitting in place as you tighten the retaining nut.
- Install the rest of the tub drain pieces onto the new drain fitting. The fittings required may vary, but it often involves using 1 1/2" female adapter screwed onto the drain tailpiece, using plumber's tape on the threads for a water-tight seal. You may need addition pipes and fittings to complete the connection, but where possible use trap and pipe pieces that are all the same diameter to help the tub drain faster.
- Tighten the trap nut, then have someone fill up the tub and drain it while keeping an eye underneath to check for leaks.
NOTE: An alternate way to install a tub drain is to use a flanged tailpiece and an 1 1/2" tubular trap with a trap adapter to convert back to the 1 1/2" drain pipe. The slip-joint washers are easy to use, and closely resemble those used under kitchen and bathroom sinks. This will make it easy if you are having trouble lining up or connecting the tub drain in any way.
One potential problem with using 1 1/2" tubular pipe is that the tub will not drain quite as fast because it is a smaller pipe. It also needs to be in an accessible location, since these are mechanical joints that can leak easier than glued joints. Finally, if anyone goes to snake the drain from the tub, the thinner tubular traps often break. To avoid this, you can remove the trap from underneath the tub and snake the line from there, if need be. A tubular trap is not the best drain size for a tub, but it rather commonly used, even in normal tubs with waste-and-overflow fittings.