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I am replacing the drain and overflow on an enamel-coated steel tub with an ABS tub drain kit. The new drain shoe is ABS, and the drain/strainer on the top side of the tub is chromed metal. What kind of sealer should be used between the strainer and the tub?

I would use plumber's putty under the strainer, but noticed [Oatey's plumber's putty][2] says DO NOT USE ON PLASTIC (ABS, PVC). The putty will not be used on the underside, as the ABS drain shoe comes with a thick rubber gasket. However I cannot guarantee that putty won't come into contact with the ABS, likely in the drain threads.

For plastics, silicone is recommended, but that has other people advising against it where standing water may degrade the seal.

I'd rather use plumber's putty since that is how the original drain was installed, though in that case the drain shoe was brass.

So, plumber's putty, silicone, something else?

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Plumber's putty is used (in the modern world) to keep gunk out of cracks and little else. It's not a primary drain seal strategy. The rubber gasket is the drain seal. Putty would just aid in cleaning around the drain flange. Silicone caulk isn't useful at all in plumbing.

Therefore, I tend to use neither unless there's a substantial gap you want to plug for aesthetic or sanitary reasons.

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  • I realize the strainer doesn't really need to be sealed, but couldn't screwing it in bare scrape the enamel and make it more difficult to tighten? The manufacturer of the drain suggested oil-free plumber's putty or silicone caulk, but did say something should be used under the strainer. Also, when I mentioned the back of the steel tub has a rough texture, they suggested some putty at the overflow gasket as well. Their gasket is flat and seals against the outside tub surface while the previous drain used a bevelled gasket inside the hole.
    – adatum
    Aug 3 at 19:52
  • You shouldn't be spinning that part. Spin the other part.
    – isherwood
    Aug 3 at 19:53
  • Spin which part? The strainer is spun from inside the tub, yes? The shoe under the tub has no room to spin, plus the rubber gasket on it will make it difficult or get damaged. In fact, that was one of the problems with the old drain. The drain was probably tightened crooked, then twisted, because the gasket was torn and dislodged.
    – adatum
    Aug 3 at 20:29
  • I assumed a nut below. Usually a fat washer is accompanied by a thin steel washer and a nut. At any rate, you won't damage the enamel unless you go nuts with force.
    – isherwood
    Aug 3 at 20:31
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    Fair enough. As we've seen here, this is a rather subjective question. You don't need putty, but you may want it. You do you. :)
    – isherwood
    Aug 3 at 20:34
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I too, prefer plumber's putty, but the general consensus is don't use it with plastics.

"the ABS drain shoe comes with a thick rubber gasket"

I believe the gasket is to provide the seal...nothing else is needed.

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    Seems the other option is oil-free plumber's putty.
    – adatum
    Aug 3 at 20:32
  • Clarification from the manufacturer: the gasket between the drain shoe and the bottom of the tub provides the seal to the outside of the tub, but the seal below the strainer is to allow the tub (and stopper) to hold water in the tub, otherwise it could seep from under the flange and through the threads into the drain.
    – adatum
    Aug 9 at 19:41
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I called the drain manufacturer (OS&B) and the technical support said to use oil-free (often indicated as stain-free) plumber's putty or silicone caulk/sealant under the strainer.

They did advise against regular oil-based plumber's putty with ABS since it will cause cracking and failure over time.

The purpose of sealing under the strainer is to allow the tub to hold water (with a stopper). Otherwise there could be seepage below the strainer's flange, through the threads, and into the drain. It is not a concern about external leaks, as the external seal is made by the rubber gasket between the drain shoe and the bottom of the tub.

EDIT: I called Oatey to double-check, and they advise against using either regular or stain-free/oil-free putty with ABS.

Their product catalog listing of both products explicitly says "not for use on ABS":

enter image description here

Oatey recommends their silicone sealant for use on ABS:

enter image description here

Though the stain-free/oil-free putty product information says "great on plastic".. go figure:

enter image description here

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