They don't need a small hole drilled in them, this was a common practice when stats were fitted with jiggle pins, to aid in keeping trapped air locks to a minimum, so long as the degas tank pipe is nice and clear just allow it to get fully warm then cool, next day level will have dropped a bit top up job done, keeping the cap ON makes this much more likely to work properly than leaving it off, it uses the pressure differential to literally suck the air out.
tabetha