It was trickey the first time I used 2 oil compounds so I'll post what I do now
It might help some newbies
EG: 1ml Test E and 1ml Boldernone
1) Wipe both vial plugs with an alcohol wipe
2) Attach a 19 gauge needle to a 3ml plunger
3) Draw up 2ml of air
4) Push the needle into the Boldernone and inject 1ml of air
5) Remove the needle from the Boldernone then push it into the Test E
6) Inject the other 1ml air into the Test E
7) Tip the vial upsidedown and pull about 0.5ml of Test E
8) Push and pull the plunger till all air bubbles are gone
9) Now draw in 1ml of Test E
10) Remove the needle from the Test E and push it into the Boldernone
11) Tip the Boldernone vial upsidedown then draw in 1ml of Boldernone
12) Remove the needle from the Boldernone
13) Draw in a small air bubble to clear the needle
13) Remove the 19 gauge needle from the plunger and fit a 23 gauge needle
14) Now your good to go

PS I suppose if you wanted to be really anal you would wipe the needle at step 5 and step 10 with an alcohol wipe