After a few mishaps with krausen finding its way up the hose to our spunding valve (with our former fermenter), this “krausen buffer” was designed to give a little more head room.
The extra PET bottle is another layer of security in terms of volume, but not least so that we can see if the Cornelius keg has been filled up.

At the time of writing this we have not filled the F80 with more than 50L but we plan to do 75L at least next time (max recommended volume for the F80 is 80L and the total volume of it is 86L).