After bathroom remodel and new vanity sink & faucet installed, I have a slow drain - but mostly for warm water only? There isn't a clog. The push down/pop-up appears to be sitting high enough. Cold water drains easily and does not back up past the pop-up, however, Warm water does not drain easily and does back up over top of the pop-up -- very strange.

All my faucets have the lever in back and I've never had any damage to my cabinets from water leaking down the lever. I think it's highly unlikely that anyone will be reaching that far back with wet hands to turn the water on and off and if someone decided to use the lever, they probably have dried their hands before they reached back to open the stopper for drainage. From my observation, kids tend to just grab the edge of the handle when using that type of handle. Plus, the design of the faucet handle allows any water droplets to drain back toward the sink.

To be clear, it’s not bubbling when I flush a toilet, and it doesn’t smell like sewer gas. I noticed the sink does not have the vent holes opposite the faucet. The PVC beneath also has the attic AC unit’s drip line feeding into it before the P-trap. Is this common? Is this why the drain bubbles? I have two identical sinks in the other guest bathroom, and neither does this. Do they have something special that allows them to catch air when needed? I don’t see anything special around the PVC.

I honestly don't understand the gas chamber mantra that gets tossed around here. We are physiologically designed to be more sensitive to and more disgusted by the waste of other people than our own. So anytime a person is forced to occupy a space that recently contained someone else's waste it is unpleasant for them. The best way to make it more pleasant is to limit the time any person might have to spend in a room where someone else's waste has recently been. The easiest ways to do that is to limit the purposes of the room used for waste or schedule waste activities so there is no overlap. Increasing the space to dilute the odors doesn't really work that well. If you don't believe me, take a walk near a cow pasture.