Just because that vial of sodium chloride, or sterile water comes with the HCG, doesn't mean you have to use that to mix it with. I believe they include that 1ml ampule of sodium chloride or sterile water, with the HCG, for women who may inject 5000iu's in one shot. Like you said yourself, Bacteriostatic water is what you and most other people use to mix the HCG, and your best choice.

An easy way to mix your 5000iu vial of HCG, is to mix it together with 4ml's of Bacteriostatic water, in a 5 or 10ml empty sterile vial. You said you used it before, so I'm sure you know the particulars of reconstituting HCG, like not squirting the Bacteriostatic water directly onto the HCG, and instead letting it roll down the side of the vial, and not to shake it and instead roll it between your hands.

Each line on an insulin syringe equals 10 units, so each 10 units is going to equal 125iu's of HCG, and therefore, depending on what exactly you're using the HCG for, an average dose of 250iu's would equal just 20 units or the second line on an insulin syringe. A 500iu dose, would obviously equal 40 units on an insulin syringe.