He has Juliette March on all-fours in a cage and the giant enema bag next to her really gives the plan away. He is going to fill her ass with fluids until she is ready to burst, make her hold it in until she has begged enough, and then humiliate her.
It's just a way to clean her up before he brings her inside. He doesn't need some dirt covered slut making a mess in his barn. It is almost ironic, then, when he pulls out his cock and makes a mess of her face.