Something you might want to consider doing rather than using multiple syringes which is a lot of hassle:
Get a pack of 14ga blunt tip needles and dispose of them or soak them in hot soapy water or something when you are done, that way you can use the same syringe and just swap the tip between concentrates etc.
Not ideal, but could be a little easier than what you are doing right now. If you are interested, they are included in our accessory kits. (There's an image on there too if you want to know what they look like)
That would just add extra cost, I already have spare new blunt needles lying about. Some syringes I use with concentrates if I am making myself a 100ml. So then I have to clean that syringe out properly.
the easiest way I have heard of doing it without any of this carry on is to use the scales and mix the bottles using weight ratios. I just haven't gotten round to doing this yet