You don't!

I don't wash pre-cuts either, but my guild is having a swap this year for 2.5" batik strips. Not knowing the quality of all the batik strips I'll be getting (14 per months for 12 months), I'm sure I'll need to wash them to test for bleeding. Thanks for the responses, everyone. Now I need to order a salad spinner!!

Thank you everyone for all the information. I think I will be doing the fabrics by hand and using my salad spinner.

Thanks again,
Barb130

Most pre-cuts are cut to a certain size. Not bigger. When you wash cotton, it shrinks. A 1 to 3% shrinkage can affect the size of a quilt. So if you wash pre-cuts be prepared to purchase more fabric at the same time to be able to finish the quilt. I personally don't prewash precuts - ever.

pre-washing (precuts) is seldom advised-
if you are set on doing it- a mesh bag would be advisable- but be prepared for your charms to no longer be 5" squares- and some may be quite (wonky) with pre-cuts it is recommended to use them as is- then wash the finished item-
if they are batiks/handdyes and bleeding may be an issue you can do a color test to see if any are going to run- and either pre-wash them or remove them from the mix-
but you will be happier in the long run if you do not pre-wash your pre-cuts=
many quilters do not purchase pre-cuts because it is best to not pre=wash them=if they are an (avid pre=washer)