no such thing as use twice,already piercing rubber twice and then the skin,as someone mentioned you only risk bruising or infection.
Trust me when I tell you that I know you shouldn't reuse pins.
HOWEVER, my recent shipment of pins was late and I had 3 pins to get through 3 days.
So I would use the pin, then rinse with alcohol and reuse a few hours later.
One pin in particular when though about 5 vials and 2 skins and was not any worse than the first pin.
In no way am I saying it's OK to reuse a pin, but if you must then only reuse within the same day and push rubbing alcohol through it before you refill it. Here is a excerpt from my peptide log thread.
"Finally got my new pins... Was getting sick of reusing the same one all day.
Here is something to note though... For people that question how much does a pin dull after being pushed through rubber and skin. Well, I know it dulls some, but the other day I had a 30g pin that went though 2 vials then skin, then 1 vial and skin and finally 2 vials before the final skin. So that's 5 rubber tops on a vial and though the skin twice and on the 3rd pin it didn't hurt much more than normal at all. Just my 2 cents."
BTW, these are BD ultra-fine 30g, 1/2" , 1ml
http://www.steroidology.com/forum/peptide-science/617731-peptides-injury-log-2.html