SpudFiles

So, I have two Sodastream bottles that have gone past their expiration date. I do NOT use them to make the bubbly water, I use the glass bottle to make the water, then I pour it over into the plastic bottles and store in the fridge.

Do I still need to discard my plastic bottles even though I do not, and will never use them to make the water?

You should discard the plastic bottles once they are past their expiration date, even if you don't use them with the Sodastream. Expired bottles may not hold carbonation effectively and could pose safety risks.