A clogged bathtub trap is a bigger problem to fix, but not impossible. Unfortunately, it does mean some extra work.
Before you assume that it is the trap you want to make sure that you to check a couple of other things. Two common problems with bathtub drains are hair in the strainer and a stuck or broken pop-up assembly. See the articles 'Fixing Bathtub Drain Clogs' and 'Repairing Bathtub Drain Stoppers', for more information and instructions.
Locating a Bathtub Trap
Bathtub drains have traps to keep sewer gas from getting into the house. For a bathtub that has a basement or crawl space below it you may be able to see it from below. When the house is built on a slab or for an upstairs bathtub, there should be an access panel on the opposite side of the wall. This might be in a closet or bedroom wall in the room that is on the other side of the drain end of the tub.
Unfortunately, this trap differs from the ones under your sinks. Usually the fitting are glued or soldered together and do not come apart. For a clog in the trap you will have to run a snake through it. I do not recommend drain cleaners. Very bad chemicals that are not environmentally friendly is one reason. The other is that they don't work that well.
Bathtub Trap Clean Out
Some bathroom traps have a clean out plug on them. This a nice feature and makes cleaning out the trap much easier. The clean out plug will be located at the bottom of the trap. Before you remove the plug you want to have a pail underneath that will catch the water.
If the bathtub is full of water, it is not a good idea to use the clean out plug. All of the water in the tub my come gushing out. With a full bathtub, you want to snake out the trap, see below.
Using a Snake On a Bathtub Trap
The bathtub drain is usually in close proximity to the larger main line that the toilet is hooked to. This means that you don't need a long snake. Generally less than 25' in length. It should be a small snake, one that is suitable for a sink line.
Accessing the Snake Entrance
Do Not try to snake a bathtub drain through the drain in the bottom of the tub. There is no way to control which way the snake will go. In addition, the strainer opening is too restrictive to get a snake through, it will bind the snake and may cause it to twist.
Do Not try to snake a bath tub drain without removing the pop-up assembly. The snake will catch on the assembly and may ruin the linkage, the snake or both.
Take off the cover for the overflow and remove the linkage and plunger for the stopper. This is normally the spot the has the control for the drain, either a lever or a dial that causes the drain to operate.
Using the Snake
Run the snake down through the opening. The toughest part will getting through the trap. Apply pressure and turn the snake until it twists through the trap. Try to judge the distance you need to go to get to the stack behind the toilet.
Run the snake through a couple of times. If the tub has water in it, the draining of said water is a sure sign you have been successful.
Checking the Drain
If you do not have water in the tub, try running water into the tub and see if it is draining. If so, put the pop-up assembly back in and fill the tub part way. Let it drain out with the water running.
Water Running Out Slowly
If you have snaked the drain and made sure the 'Bathtub Linkage' is working correcly, then you may still have some issues at the strainer, see the article 'Bathtub Drain Clogged' for information and instructions.
Got it? Water going down? Great this clogged bathtub drain problem is solved.