Air vent for Coleman water jug

thingiverse

Coleman water jugs from the 1980s had a plastic plug that would partially pull out to let air into the jug (to avoid a "glug-glug-glug" when pouring). The design of this plug was flawed, it had a sharp transition between round and square profiles. Over time this point would accumulate stress fractures, and the plug would break into two pieces. This redesign smooths out the transition so that there are no concentrated stress points. There are two designs here. The simple one ("Whole") prints vertically. However there's a concern that in this orientation the layers may separate in use. Thus there's a second design ("Half") which has two halves of the plug printed horizontally, then you must superglue them together.