best way to transfer glycol into chiller loop

Bluetech

I have to replace a pump on chiller loop and will meter water into system to find gallons the system holds, what is the best way to transfer propylene glycol into the system to get the ratio ? I have never had to do this, but have heard diffferent ideas, I know I need a transfer pump and have a refractometer how do I introduce this into the system? any help is appreciated.