Plumbing – this silver plate beside by tub and what is it for? Why is it leaking? What to do

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So I was draining the tub in my 1920's era condominium a moment ago when I noticed a substantial amount of water pooling on the floor next to my tub. I soaked it up in a hurry but then I noticed a little more bubbling coming up from under this silver mystery plate next to the tub:

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I've used this tub many times before but never had an issue. As soon as the tub had fully drained out the water stopped coming out from under the plate.

What is happening here? I'm totally befuddled. What should i do?

Best Answer

That's a cover for your drain clean out. If water is leaking out of there then either the threaded cap below, if there is one, is loose or there is a blockage starting to form and the drain water is starting to backup because it can't go down the drain fast enough. There could also be a drain plug under the cover that has deteriorated and is leaking. You can undo the screw on the cover and check it out and see what the problem is. Take some pictures. Then come back here for some solutions. Here's what the drain plug would look like.

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