All coins in, drop into a hopper. When the hopper gets full, it overflows into a bucket below the hopper.
If you hit a jackpot, it is paid out of the hopper.
The bucket is taken out every couple of days and taken to hard count.
Coin in is counted.
Coin out is counted.
Hand pays are subtracted.
Fills are subtracted.
Result = drop

Yes if you can get the machine to take a foreign coin, it can be paid back out.
Hard count seperates all foreign coins.