I knock mine into a Grindenstein, which are sold by several site sponsors. It holds 5 - 8 pucks in it. Empty if once a day, and its quite clean. Can go through the dishwasher, or be rinsed under hot water. I find its a good compromise between a big knock box, and putting them down the sink.
First sponsor hit on google: http://www.coffee-a-roma.com.au/shop/en/accessories-3/grindenstein-knock-box-29.html