Playing horde round about the wave 40 mark you should get all 4 power taps available to spawn, spawn each of them like you would in King of the hill, by standing in the circles. To do this faster do this on beginner, just so you won't die so quick. And AFTER the wave has started get 4 players in your team to stand by them then press and hold X until you claim the fabricator power, should pop a minute after. EASY!
Quick edit. You cannot do this without 4 people in your team. One power tap per player. It won’t work if one person collects power from multiple power taps.
Also this cannot be done if one of you is playing as Jack in a 4 player team if you are in a 5 player team and one of you is jack then you can get it, just made an edit, cuz some people aren't understanding this.