To cover someone, something, or oneself in soap. A noun or pronoun can be used between "soap" and "up." To conserve hot water, I turn the shower off while I soap up and then turn it back on to rinse off.Our dog hates it when we soap him up for his bath.
soap up
v.
1. To cover someone or something with soap: We soaped up the car, scrubbed well, and rinsed it clean. I soaped my legs up and shaved them.
2. To cover oneself with soap: I soaped up and rinsed off in the shower.