Place the straw in with the all rubber side down. Make sure the white funnel cap is placed over the top of the small rubber end at the top of the bottle. Then you will line the top of the straw with the hole in the cap and screw the cap on
I’d try boiling water. In the future, I don’t recommend washing this. I pour water from this into a smaller bottle to avoid my backwash entering the bottle while still using this as a measuring tool to my intake.