Drain Cleaner

Drain Cleaner is an achievement in Halo Wars unlocked on the map Memorial Basin. To earn it, a player must kill twenty enemy squads with a continuous Covenant Leader Power. One tactic to get this achievement is to use the Arbiter's rage mode against an army of infantry since the Arbiter in rage mode can be difficult to take out.

Strategies

 * 1) One solution would be to make a 1v1 match. It's best to use the Reinforcements gametype. If you're using any other gametype, you should increase the difficulty so they train more units. Next, pick the Arbiter. The enemy can be anyone you want since it's a Reinforcements gametype. When the match starts, build a Temple and the rest Warehouses. All you should do now is just keep researching the Arbiter's skills and capturing the bases close to you. The bases you capture should all be Warehouses. Once you have all the upgrades for the Arbiter and a fair amount of Warehouses, keep all your reinforcements at your base for protection and uses Arbiter's Rage. You should have a good enough income to keep the rage on the whole match Once it's on, just keep running around the map killing everything you can. Remember to not get out of Rage Mode. You should have this achievement in no time.
 * 2) Another method to this achievement is much easier and faster. The game should be a 1v1 skirmish match with you using Arbiter, and the A.I. using anybody set to normal difficulty. For this method to work you must be in a death match. The first thing to build is your temple because the sooner you have him attacking the better. Fill the rest of the spaces with shield generators in case you are attacked while you are gone. By the time you get the achievement you should only be attacked once or less. As soon as Arbiter is out, send him to the first extra reactor in rage mode. Destroy all the enemies there and continue to the next reactor on the map. Since you are playing on a death match, you already start with a ton of resources and an upgraded leader. Destroy all the units on all of the extra reactors scattered on the map and then head to your enemies base. If you did this quick enough, he should have only a hand full of units, but that is all you need for this achievement.

Note: You may not want to do this against a UNSC because of the possibility they will drop a disruption bomb, but on normal difficulty you may not have that problem.