The best way to do this is on Easy difficulty with all scoring skulls on except for Blind, so you can see your health. There are two health packs in the area, one in the building and one down by the pipes in front of it. Try to resist the urge to grab one unless your health gets down to low yellow or red. From the start kill off all the Grunts and start meleeing Elites. You will likely need to turn your look sensitivity up to 7 or higher so you can punch them in the face then circle strafe around behind them for a beatdown or assassination.
They will die faster if you can do the assassination as you dont need to drop their shields, but the game is awful finnicky. Even if you hold down your melee button from behind them, sometimes it will only do a melee. After a while, golden Elite Ultras will show up. Some will have Concussion Rifles, while one or two at a time will have Energy Swords. Focus on the sword ones first. As long as you keep your sword ammo replenished by killing sword guys and picking up a new one when the current one runs out, this grind is relatively easy if somewhat tedious. The easiest way to assasinate the gold ones is to punch their face and wait for them to do the roundhouse kick animation. While they are doing this spinning kick, strafe to YOUR left (their right) so that you are behind them and facing their right shoulder. Press and hold melee to assassinate.
You are mostly safe inside the building at the map's raised center as Wraith blasts won't be a worry. However make sure to move away from your current fighting spot and throw a grenade into it once or twice to detonate all the grenades scattered about from your killing frenzy on the Elites. It took me 95 minutes to reach 189,000 doing this method. It may seem daunting at first but once you get a feel for it, it's quite easy to go on killing forever.