Yeah, use a 18 or 20 guage needle...... This is how I personally do it...
Keep in mind I preload like 6 syringes at a time so I dont have to fool with vials every week.
Place 1 18g needle in the test vial and one in the deca vial.
Take syringe, screw it onto the needle in the test vial, draw desired amount
unscrew and immediately screw into deca vial, draw desired amount,
unscrew and screw your inj. needle to the syringe.
Keep in mind to do this as cleanly as possible, some people dont like to leave a needle inside a vial due to the air getting in the vial, I for one have never had a problem, Im still alive!
Good luck!