My house has a flat roof and leaks, mostly directly underneath the drains.
I've had problems with leaking around the drains since I've owned the house, mostly dripping, but over time it's turned into gallons of water.
Last year I installed a foam membrane which is basically indestructible and totally leak-proof, but I'm still leaking. (the new roof stopped an unrelated leak in a different part of the house).
I think I've narrowed the leak down to the drain in the upper left of the picture. I think the leak is below the roof membrane, but above the roof decking (it's very hard to tell). The drain has a small bit of chicken wire rolled up in it to keep out debris.
My question is, why do I have two drains so close to each other (they're about 18 inches apart), and is there a reason that I couldn't just seal off the one that I think is leaking? Both drains appear to drain into different pipes, one of which (upper left) has a toilet pipe connected to it in the basement.
The house was built in 1928. Based on the technology level of the drain on the lower-right, I presume it was installed sometime after the house was built (?), or at least someone upgraded it, without upgrading the other one.