I draw and inject with 20 G.If you are drawing out of the same bottle repeatably,draw with 23G needles.20G tear up the stoppers.As far as needles, I buy them in boxes of 100.
20G for drawing and injecting(oil based)w/5cc syringes
23G for drawing out of same bottles w/5cc syringes
25G for drawing and injecting H2O based.Hope this helps you.Never re-use the same pins or syringes.There to cheap to take the risk.