How do you wash your hair with a bonded/sewn in lace wig on?

I am new to lace wigs and love them! I keep reading about how with the right methods or adhesives, lace wigs can be bonded/sewn in for as many as 6-8 weeks! This is wonderful and amazing. But if you have hair underneath, it's going to need washing at some point, otherwise your scalp is prolly gonna itch after that much time. I realize your hair is covered and isn't going to get dirty, but the oil comes from inside. How do you wash your hair with it semi permanently attached?