20 to inject??? Ouch,,,,
Tons and tons of advice can be given here. I have been doing what I do for yrs and it works for me.
For oils I use a 20-21 to draw it out of the amp/bottle. For injecting I use a 25. I take the 20g syringes w/the oil in them and soak them in some hot water. I like the water temp wise just right before it's starts to boil. So on my nuker it's around 3:50 sec anyway, take the cup out of the micro, soak the syringes in the hot water for about a good 4-5mn is all. Pull one out, take the 20g tip off and screw on a 25. I promise you the oil will pass through no prob. It will be slow but it will flow fine. Less scar tissue in the end my friend...