suds up

1. To create, fill with, or be worked into a foamy lather. If the soap isn't sudsing up, it means you aren't using enough water. Only add a bit of detergent, as you don't want the water to suds up too much.

2. To cover someone or something with soap lather, as while washing. In this usage, a noun or pronoun can be used between "suds" and "up." Make sure you suds up the outside of the car really thoroughly. She plonked the two kids in the bath, grabbed a washcloth, and promptly started sudsing them up.

3. To wash one's hands, face, body, or hair with soap or shampoo. You kids are filthy! Both of you go suds up straight away and then come down for dinner. You shouldn't be sudsing up more than two or three times a week, otherwise you'll strip the natural oils out of your hair.