Every time someone passes, another die is placed on the dustbin.
This statement is a bit misleading. There is not one die per player passing, but rather one die for each time any player(s) have passed on using the current pool of dice. If multiple players have passed on the same pool of dice only one die is placed in the bin then they are rerolled and everyone who passed chooses a die or passes again. Regardless how many players pass again only 1 die is placed in the bin with the remaining dice rerolled.