A simple stopper for common hot water bottle.
I'll be very happy to see someone with OpenSCAD knowledge make a parametric remix of this file. I don't have the skills unfortunately.
This particular one is a M24*4 thread, but it can be easily tweak to your own bottle opening by editing the dimensions in solidworks (thread feature requires 2016+).
I wouldn't recommend using a low-temp material, however a 4 walls - 10 bottom layers PLA part as survived so far without failure.
Maybe use this as a temporary replacement while waiting for a proper plug.