Plumber's putty or silicone for tub drain?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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":

Oatey recommends their silicone sealant for use on ABS:

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