Only if the fabric is considered washable, & you want to be able to wash it after you make up the kilt.

If the fabric is dry clean only, you can have it dry cleaned, dry clean it yourself if your dryer is large enough, or dry clean it at a laundromat. If it is dry clean only, you can try hand washing it in a tub & air drying it.

Cleaning by whatever method before you make up a garment is SOP because if the fabric is going to shrink, you want it to shrink before you do any cutting on it.

Sherry