What are the design limits of a normal tub overflow drains (and their gaskets)?

Question

We have a leak from the tub into the ceiling below. I'm pretty sure it's from the overflow drain, but as soon as the home warranty plumber heard this he said "oh, that's the problem, the overflow gasket is not designed to take that much water" and basically washed his hands of the issue (and emphasized his great experience as a master plumber vs. mine [none]).

But this sounds crazy to me: my expectation is that an overflow drain should be able to take as much water as will flow through it without leaking. I agree it may not be able to prevent the tub from overtopping, but I do expect it should not leak unless you're pointing a pressure washer nozzle through it or something.

So am I crazy, or is he?

Answer 1

Wow, he might be right... according to this, "overflow drains" are a complete misnomer and the whole assembly is YMMV/at your own risk/a farce:

According to PMI (Plumbing Manufacturers Institute) no manufacturer currently makes bathtub overflows, only trip lever assemblies are made.

...

If you disagree then I challenge you to come up with the documentation that these so called overflows are a real plumbing product in the same sense as any other plumbing product being what it claims to be:

• Show that a standards specification exists with ASME, ANSI, NSF, IAPMO, or any other approved standards making group.

• Show the documentation for the engineering calculations that specify the flow rates the overflow should be capable of handling and how this relates to the overflow "protecting against accidental flooding resulting from an unattended filling operation".

• Show what listing agency is providing a listing for such a product and what testing protocol they are using to verify that the overflow is meeting the standard.

• Show what manufacturer makes an overflow that has such a listing and stands behind the product with a warranty that the product will "protect against accidental flooding resulting from an unattended filling operation" according to the standard to which it is listed.

You will find that none of this exists.

Yikes.

Answer 2

no manufacturer currently makes bathtub overflows, only trip lever assemblies are made.

Well, on this side of the pond, bathtub manufacturers describe items such as "BATH EXTENDED POP UP WASTE & OVERFLOW" and "BATH WASTE AND OVERFLOW"

These items are sold as overflows. I'm pretty sure that if a vendor describes something as an overflow, or a plumber installs something they describe as an overflow, they can be prosecuted if it is a deliberately misleading term.

The statutory right under section 9 (goods to be of satisfactory quality) will only be breached if goods are not of the standard which a reasonable person would consider to be satisfactory, taking into account circumstances including the price and any description given.

- http://www.legislation.gov.uk/ukpga/2015/15/notes

If something described as an "overflow" leaks, I believe a reasonable person would consider that unsatisfactory. IANAL.

Just because there are no government mandated rules or standards covering a specific item does not mean that manufacturers, vendors and installers are free to use misleading words to deceive the public and/or to supply or install plumbing that leaks.