Turn a utensil container into knock box. Way better than banging your portafilter in the sink, and cheaper than a retail one.
This method can be used with any container with a wall thickness of .5" to .75"
I used my wife's "Giadia Bamboo Utensil Holder" This has a wall thickness of .75"
A big section of pvc pipe works too.
I picked up all the supplies at my local Lowes.
-length of .5 inch copper pipe
-Two .5" cooper pipe caps
-clear tubing (reinforced)
-rubber grommets (i found an assortment pack that had two .5 inch grommets)
-index card (for transferring cut line)
-1" bit (I used a spade or "paddle" bit) This is based on the outside diameter of the grommets' inner ring...
-clamp (quick clamp or pipe clamp)
-hacksaw (or Dremel)
-crosscut saw (chop saw if you have it)
-safety stuff, glasses gloves and a mouthgaurd
-fine sand paper