For the time it takes to empty it. In Germany we can buy 100ml injection water in a bigger vial. Looks like a peptide vial filled with water but bigger. All I do is I take off the cap, inject 1ml benzyl alcohol, shake it, and use it whenever I need some BAC water.
In Germany these things are dirt cheap, I guess they are cheap and easy to get in every european Country. I attached a pic with the vial and the price (3,50€ total with shipping included for 100ml). And we can buy 10ml and 50ml of benzyl alcohol for a few euros, too. That 50ml bottle of benzyl alc will last forever possibly.
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