Step 1: What you need
A small dirty jar that needs to be cleaned
Warm tap water (not pictured)
Liquid dish soap
This technique is also fantastic for cleaning bud vases or salad dressing cruets as well.
If you do not have plain rice on hand, coarse salt or quinoa may work. I have not tried them for this purpose but they seem small enough and should be abrasive enough to do the trick.