I want him to lube up her pussy with his tongue. Then for them to go into a 69 with her on top. He can lick her clit as I take her from behind, occasionally I will take my cock out of her and put it deep into his mouth to remind him who is in charge. After I unload in her I expect him to clean both of us up with his mouth. If he misses one drop (if a drop hits his face or the floor etc) then he doesn't get to cum.