Thx for the tips TimeLord!
I managed to drill the plexy without developing cracks, problem is how to make them not appear later, when you screw the barb in. I used some liquid semi-permanent Loctite sealant, and it works well, but tiny 'cracks', visible only under certain angle inside the structure of the plexy appeared week or so later. No leaks, just hardly visible changes inside the plexy.
I'm gonna use some lubricant next time I cut the threads in plastic, and it will not be olive oil (hmmm, fish, anybody?
)
Think that I cannot find mill bit that is 14.5 mm dia, I'm gonna try to make somethin similar from a extra drill bit I have.
Thx!
Cheers!