So you have a few options
If all the beers that are included in the bucket are on the same menu group Create an Item for beer bucket and create a new modifier group.
When you go to add modifiers say use existing menu group
Set it not to be priced and set the price on the bucket and adjust your min/max choices.
If you have specific beers you want to use create new modifier from exiting item. Both ways will keep inventory in line
