In our master bath we have a stand-alone, single handle shower. Intermittently, after the shower is used, we get a delayed drip. Sometimes it's within a half hour and sometimes it happens several hours later. It may happen multiple times between uses. At times it’s just a little water or at others it’s two cups or more. I’ve changed out the cartridge without effect. It’s as if the pipe to the shower head above the faucet is emptying out, but I can’t figure out what is pushing the water up and out of that vertical pipe. Everything else in the house drains okay, so I doubt it’s a venting issue.

I purchased one of the big box store Foot Lok Stop Tub Drains, the push down type. I removed my current 1/2 drain. When I screw in the new Foot Lok Stop Tub Drain I get two or three turns and it will not screw in any further. Both drains, old and new are 1/2 drains. What am I doing wrong? Thanks in advance