I have a Kohler Wellworth (low flow model) that uses a canister-style flushing mechanism. The tube that comes from the fill valve is to be seated/secured in an opening at the top of the canister, held in place by what I assume should be a snug fit. However, the hose continually pops out of place after flushing. Is it safe & effective to glue a hose like this in place? I can't see a place that a typical clip could be used to hold it in position.
Assuming you're talking about something like this:
and that the tube is connected to the protrusion at the top, I would suggest a simple hose clamp to hold it in place.
They come in a wide variety of sizes and one small enough to fit that would be pretty cheap. Just don't over tighten and crush the input fitting.
A zip tie might work, as well, and they are as cheap as can be, and when you're using one small enough for that fitting, it's hard to pull on it hard enough to do damage.
If the larger portion of the fitting is still in place, push the tubing on far enough to reach the top of the canister itself and a very small amount of pressure around the smaller diameter portion (from either the zip-tie or the hose clamp) will be enough to squeeze the tube so that it can't slip up over the larger diameter.
Try one wrap of electrical tape around the tube. If that ever fails, move on to hot glue (or try two wraps).
Try nipping a 1/4" or so off the tube, if there's enough slack.
Try detaching the tube and reversing it.
No need for zip tie or hose clamp. Instead wrap a twist tie around tightly and twist the ends to secure. If there's room, add a second one for extra security.