Why Boiling Water Is the Wrong Move on an Old Tub Drain

The internet’s favorite drain fix is fine on a modern kitchen line and a bad idea on a tub in a pre-war Shore house. Here is what to do instead, and where the clog actually is.

Search how to unclog a bathtub and the first suggestion you will get is a kettle of boiling water. It is on every list. It costs nothing, it feels like doing something, and on a kitchen line with a light grease film it occasionally helps.

On a bathtub it is the wrong tool for two separate reasons, and in an older Shore house the second one can cost you a ceiling.

The short version. Tub clogs are hair, and hair does not dissolve in hot water. Meanwhile boiling water is hard on old waste assemblies, old joints, and anything plastic in the last two feet of the drain.

Reason one: it cannot work

Grease melts. Soap scum softens. Hair does neither. A tub clog is a mat of hair bound together with soap residue, and the hair is the structure. Take the soap out of it and you still have a mat of hair sitting across the drain.

People pour the kettle in, the water drains a little faster for an hour because the soap loosened, and then it is exactly as slow as it was. Two weeks later they do it again.

Reason two: what it does to old plumbing

A lot of houses on the Shore were built before 1940, and plenty more were plumbed or replumbed in the decades since with whatever was standard at the time. Between the tub and the floor you may have any of the following:

• A plastic waste and overflow assembly, common in anything fitted since the seventies, which is not rated for a kettle of water at full boil poured straight in.
• Old galvanized pipe with a heavy scale lining, where a sudden temperature swing can shift the scale rather than clear it.
• Cast iron with a lead and oakum joint, which does not enjoy repeated thermal shock.
• PVC with solvent welded joints, which are fine at normal drain temperatures and are not designed for water at 212 degrees sitting against them.

The failure is rarely dramatic. It is a joint that starts weeping, into a crawlspace or into the ceiling of the room below, and that shows up months later as a stain. By then nobody connects it to the kettle. If you want to put hot water down a drain, hot tap water is plenty and it is safe.

Where the clog actually is

This is the part that saves people money, because the blockage is almost always within reach.

Most tubs on the Shore use a trip lever: the little flip switch on the overflow plate at the head end. Behind that plate is a linkage that runs down inside the overflow tube to a plunger or a pop-up in the drain. It is a metal rod hanging in the pipe, permanently, in exactly the spot the hair goes past.

To get at it:

1. Unscrew the two screws holding the overflow plate.
2. Pull the plate straight out, slowly. The linkage comes with it, and so, usually, does the clog.
3. Clean everything off it. A bucket and rubber gloves make this much better.
4. Feed it back in carefully, seat the plate, and do the screws up.

If your tub has a lift and turn or a push stopper in the drain itself instead, that unscrews out of the drain body and the same principle applies.

With the stopper out, run the tub. If it drains properly you have solved it for the cost of ten minutes. If it is still slow, the blockage is past the trap and it wants a cable.

What not to reach for

Chemical drain cleaner. It will sit on top of a hair mat doing very little, corroding whatever it is sitting in. Then it is still there when somebody opens the line. We would rather arrive to a blocked tub than a tub full of caustic.

A wire coat hanger. It scratches the finish on the way in and it usually pushes the mat further down rather than pulling it out. A cheap plastic barbed hair tool from a hardware store does the job properly and costs almost nothing.

Baking soda and vinegar. Same answer as everywhere else. It is a fun reaction and it does not move hair.

When the tub is telling you about something else

A tub that is slow on its own is a tub problem. A tub that backs up when the toilet flushes, or that fills with water when the washing machine drains, is not. Those fixtures share a branch or a main, and the tub is simply the lowest opening in the house, so it is where everything shows up first.

If that is what you are seeing, stop running water and read every drain backing up. Running more water into a blocked main just puts it on your floor.

And if the water is draining but the room below has a stain, that is not a clog at all. A tub waste and overflow leaks when the gasket behind the drain flange fails, and that is bathtub and shower work rather than drain cleaning.

Getting it cleared properly

When the stopper is clean and the tub is still slow, the mat is in the trap arm or the branch and it wants a cable rather than a kettle. A single fixture runs $175 to $450, and if the same tub has blocked twice in a year it is worth a look at why. The drain cleaning cost guide has the rest, and the service page is clogged bathtub drain repair or drain cleaning generally.

Will boiling water unclog a bathtub drain?

No. Hair does not dissolve in hot water, so there is nothing for it to do. On an older tub it can also soften a plastic waste and overflow assembly or crack an old joint, which turns a slow drain into a leak into the ceiling below.

Where is the clog in a bathtub?

Usually within the first two feet: in the trap, or caught on the linkage of the trip lever stopper inside the overflow tube. That is why pouring anything in rarely reaches it.

Can I take the tub stopper out myself?

On a trip lever tub, yes. Unscrew the overflow plate, pull the plate and the linkage out slowly, and most of the hair comes with it. On a lift and turn or push stopper, it unscrews from the drain itself.

How much does it cost to unclog a bathtub drain?

A single fixture cleared with a cable runs $175 to $450. If the tub and a shower or a toilet are backing up together, it is not the tub, and a main line is $300 to $600.

Why does my tub drain slowly only sometimes?

That usually means the blockage is partial and further down the branch, and it only shows when something else drains at the same time. It is worth clearing properly before it closes completely.

Written by the team at Shoresteady Plumbing, Temperanceville, Virginia. Master plumbing licensed in Virginia and Maryland. Prices shown are typical ranges for the Eastern Shore, not a quote. Your written estimate is the only number that binds either of us.

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