It happens that ss formulated :
I bought a new bottle trap for under the sink, there is the tiniest of leaks,
maybe about a couple tablespoons overnight, its coming from the bottom part
(the trap) that screws on to the top part, I have tried tightening a bit more
but still drips.
Any ideas to seal it 100%, although to be honest I cant understand why it
leaks.

A smear of plumbermait on the threads will help seal it.