If the water in the pot freezes, this sacrificial plug pops out as the freezing water expands, relieving the pressure in the pot.
(this sacrificial plug; pops out; T:as the freezing water expands, relieving the pressure in the pot) (the freezing water; expands; )
this sacrificial plug the freezing water
pops out expands
T:as the freezing water expands, relieving the pressure in the pot