S5E15 : When the Levee Breaks

When Bob goes out of town, Eric and Donna decide to "practice" being married at her house. The gang is excited because they think this is a chance to party all weekend at the Pinciotti's place, until Eric and Donna are forced to set them straight. Meanwhile, Kitty goes to the jewelers to pick up a ring she thinks Red got her as a surprise. But she discovers the real surprise: it's actually an engagement ring for Donna.