How to unlock: The Drummer Boy will talk to you after completing few quests for Railroad faction.
This quest is partially a random quest. It consists of 6 objectives, but you are rewarded for each of them separately. The general concept of the quest is going to a selected location in order to clean it after previously receiving briefing from a mail box. The places you must clean are selected randomly. Enemies' level and their number remain on similar level. Other quests are unlocked after receiving reward and returning to the location shortly after - the Drummer Boy will greet you once more and give you next part of the quest.
Quest rewards: experience, random number of bottlecaps (from 100 to 200), random (usually modified) weapons/armors