| I've always used a vial of insulin until it was gone. I've never noticed a lack of potency or had any issues with discoloration or clouding which would indicate a problem with bacteria. I typically used a bottle up in around 6 weeks.
After I had my islet transplant I kept the insulin vial I had opened. its been two years. It's still clear. Of course I wouldn't use it now but it still looks normal.
I used to use syringes until they were dull and that includes injecting through clothing. I'm not sure the alcohol is all that important but if it makes you more comfortable by all means do what you need to do. | 
