Summary-don’t rock your plastic big mouth bubblers near the vertical flat portion of the bubbler where the lines are to show how many gallons are in the bubbler. If you do, the plastic may flex and eventually crack open near the base.
I had a crack develop near the base of my big mouth plastic bubbler. It happened while I was rocking the big mouth bubbler for 5 minutes to aerate the wort at the start of fermentation. I had previously noted that I could not rock this fermenter in a certain spot without the plastic flexing near the base. I got around this problem by rotating the bubbler to rock on another spot that did not flex.
For this brew, I had the stereo blasting and I was tired. I forgot to not rock on this spot and did not hear the plastic flexing. So about 3 minutes into shaking I saw a pool of wort on the floor. It was 3.5 gallon brew in a 6.5 gallon bubbler so I was able to hold it on its side with the crack up to prevent further loss. I poured it into another sanitized bubbler and was on my way.
I inspected my plastic bubblers and I believe I found a weak spot in all the bubblers. There are three stiffening rings on the big mouth bubbler. The rings are the horizontal “bubbled” area of the plastic vessel. Unfortunately, the rings do not go all around as there are two vertical flat areas of the bubbler where they put the “lines” to indicate how many gallons. If one rocks in this area as I did, the plastic may eventually crack due to fatigue. Its the weak spot of the plastic bubbler.
Stiffening rings are used on vessels to make them stronger particularly in vacuum service. The rings need to go all the way around the circumference to be fully effective.
I rock my bubblers a lot besides the initial aeration step. I rock during diacetyl rest and when I put coconut in the beer. I used to generally rock on the weak area because I orient the bubbler with the gallon lines facing me when I put them on the fermenting shelf. Not any more 
