Complex sentence: Housemates nominated face-to-face in "Nasty Nominations" in the garden, in which housemates had to pour horrible substances over the two housemates they chose to nominate.
Split into simpler sentences: Housemates nominated face-to-face in "Nasty Nominations" in the garden. To nominate, a housemate had to pour horrible substances over the two housemates they chose to nominate.