Trying to replace the bath tub spout for a front-end threaded connection, I found a "Universal" tub spout (and in fact could not find a front-end-threaded-only tub spout at the local hardware store). This spout fits just fine and installed fairly easily. However, wanting to seal the connection, this style of spout has a gap in the bottom for the "set screw" that a slip-on connection would use. How should I go about sealing the spout? How do people with spouts that use a set screw seal their connections? Though they would serve no other purpose, I could add set screw and its mounting apparatus if it would help with the seal.
Not a plumber, so just a comment: You would caulk around the top, but leave this open at the bottom so that any water that does get in there can get back out.– FreeManOct 11, 2021 at 13:08
Even when installed using a set screw, the hole on the bottom is not sealed. Because its on the bottom, any water that splashes in will just drain out, and the amount of water that can enter the hole is limited to just that - a small splash. Unless your kid is sitting there and pumping water into the hole with a water gun, leaving it open is standard and shouldn't cause a problem.
If anything you can caulk around the pipe coming out of the wall before installing the spout, but don't worry about the hole under the spout.