Your partner lays on their stomach and puts a funnel in their ass. You proceed to pour hot water in the funnel. Than dip your balls in the funnel, like you submerging in a hot tub. Your partner than sharts and farts to create the jacuzzi mud bath effect. You can do this with a sibling if you are from the south.
My sister was great at the spa, she gave me the special mud bath that was on the menu.