1. Cut out a piece of 8'' x 6'' cotton or muslin snipping off the bottom corners to the desired to the desired taper. I like to take off about 3'' Now, that measurement works best for my coffee maker
so you may want to increase or decrease according to how large yours is. An easy cheat is to trace one of your old filters just to make sure you cut it to the right size.
2. Sew your the pieces together. Make sure to do a nice tight stitch, you don't want to find a whole bunch of grounds in your coffee. No one likes a cup of coffee that they have to chew.
3. Turn inside out and you are done. Slap it into you maker, fill it with your favorite blend and enjoy.
As for washing I always rinse out the grounds and let it air dry on my dish rack. Every once in a while I will wash it in the top rack of the dishwasher.