btw,,the only mod i do to mine is to cut that airtube down almost flush with the top silicone ring on the head section,as you vape it will condensate on the inside of the tube and run down between the top air tube and the head airtube and eventually fill up full and start gurgling
i vape 8-\20 mix,,mine will start to gurgle when the tank gets close to being empty,so just refill and problem solved