Yep leaving them open is a good idea but removing the bleeding grub screw is the key to the most likely place where gas can be .
I mean the actual gas is heavier than air and will evaporate over a few days but when it reaches the gaseous state, light particles might still rise and be in that bell like area.
The bleed valve is access to the most concealed area.
I still like the thing filled with water with the valve and bleeder open for the cutting, and did a score cut right around prior to penetrating the skin. This makes less water and once cut there is no danger of creating pressure.
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