Easiest way ive seen others do it is use a multi dose vial insert into one syringe and just use bigger cc syringes if needed.

You can realistically take every compound you take (oil based) and mix them all together in one big vial. So long as the dose is distributed correctly, you just draw from one vial. No sweat brother. You're good.
Personally, I switch after I'm fully loaded. No need to waste pins, just continue doing like you're doing and change before injection. (Shit! I know a ton of dudes that don't even do that! Lol)

Using 2 different needles to draw between compounds doesn't make this any safer, gang. Technically it adds a 2nd chance to contaminate things, but that's a reach at best. both are safe, just clean your tops well and pick a nut. I do option #2, draw w 18g and pin w 25g.

I draw testosterone, draw primo, and ventroglute injection with the same needle obviously wiping everything down and being sterile. Dull needle or not i just don't want to inject multiple times or get a bigger gauge. 1ML syringe 29G needle. I'm good with what i have, inject half a ML of test and half a ML of primo every tues/thurs/saturdays.. 300mg test/week. 150mg primo/week. It's been working out for me for the last month and a half I've been on both. although in the summer i want to up the primo to 300mg so i need to figure out if i wanna do EOD injections or just bite the bullet and get a bigger gauge needle.

Aggree with aggie. What i would add is, you dull the needle by pushing it into multiple stoppers, so I do not advise injecting with the same needle you draw with.

What i do personally is wipe the stoppers with alcohol pad, use a new pad to wipe injection area, draw from vials with a 21 guage 1" then switch to 25 guage 1" for glute injections or if pinning delts, I backload into a 29 guage 1/2" slin pin.

You can do all the above and jab yourself with the same needle as long as you clean the tops of vials with alcohol first. I change the needle to pin with because it's a smaller needle and sharper.