I am looking to make a multi bottle filler. I have watched several videos and done quite a few searches but cant wrap my head around one thing. All use a pressure relief valve to regulate the bottle pressure. With the DIY beer gun on here the bottle pressure is purged whenever it equals the keg pressure and stops flow by slightly breaking the seal of the bung which makes sense as all the gas is at the top. Now my confusion comes from the fillers that dont require the bung to have its seal broken and have the pressure relief valve to purge this pressure. How is the CO2 venting out of the pressure relief valve but the dip stick in the bottle is going to the bottom of the bottle. Should this not allow beer to escape as the pressure would push the beer back up the dip stick and out the pressure relief valve? From what I see on youtube its just a barbed connection with a silicone line going through the bung not sleeved air port or anything like that. I cant seem to wrap my head around this so was hoping someone would have an idea.