You are ONLY required to pay taxes on winning if the ODDS are above 300:1. This is true in LAND based casinos all over the country! If you win 25,000 over the course of a few hours playing blackjack then you are NOT required to fill out any forms.
It is up to YOU to declare it or not. If you win the SAME 25K on a jackpot in a slot you ARE required to fill out an IRS form and have taxes withheld. Trust me on this!
As for gambling outside of the US, there is nothing required. I know for a fact that if you win $100,000 jackpot in the Bahamas or Canada, nothing will be forwarded back to the IRS in the states.
It might just be a little tricky to get the money back in the US undetected! But that is what I call a GOOD problem!