You could handwash each individual Lego block, but honestly, who has the time or patience for that? Instead, clean all of your Legos in one go by placing them in a laundry bag or pillow case (just knot the open end together or secure with rubber bands). Then pop them in the washing machine on cold water.
Note: The bricks may melt if the water is above 104 degrees. Also, do this at your own risk. Depending on how you wrap them up, the Legos may scratch the inside of the washing machine or even other Legos themselves. Let the pieces air-dry.
Image Source: POPSUGAR Photography / Kelly Ladd