Janitor

Mechanics

 * "Cleaning" only means your target's role and Last Will will not be revealed to the Town. It does not have any effect on an Arsonist's gas.
 * If there are no kill capable Mafia roles left, you will become a Mafioso.
 * You can talk with the other Mafia at night.
 * Your cleaning attempt will be successful if your target dies for any reason, including leaving.
 * The cause of death will still be revealed to the Town, which will prove their role if they were a Vigilante committing suicide or a Bodyguard dying while protecting their target.
 * Your target's role will appear as "cleaned" in the Graveyard.
 * After you have successfully cleaned a victim, you will receive a message about their exact role.
 * You will be able to read your victim's original Last Will by clicking on their name in the Graveyard. Everybody else, including the Mafia, will see a blank Last Will.
 * The Retributionist is not supposed to revive victims you have cleaned, however they sometimes still can. This is a known bug.
 * Amnesiacs cannot attempt to remember a cleaned person's role.
 * If a Forger attempts to forge your target's Last Will, their attempt will have no effect.

Selecting Someone to Clean

 * It is very important to clean Town Investigative roles because they are almost guaranteed to write something in their Last Will that is important to aid the Townies in lynching the right people. Always clean them, especially if the Mafioso or Godfather decides to kill a known Town Investigative. You can later disguise to be one of the Town Investigative role as well. Additionally, Consiglieres can benefit from the information obtained, and it will often help them prioritize their investigations.
 * Be wary of cleaning the Mafia's first target. Since night one is when Investigators and Sheriffs will only be getting their first bit of information, if you kill one of them, their Last Will will not contain useful information for the Town. If any roles that are not Town Investigative are killed, then it doesn't matter either, as the Retributionist normally waits to use their only revival past Night 3, and the Medium is almost never confirmed after the first night. As the information from these Last Wills will not surface until much later, your cleanings may be more useful to use later on.
 * On the other hand, in games with tighter role lists, like Ranked, cleaning anyone will conceal their role and make it much harder for the Town to determine people's roles by process of elimination; therefore, it might be a worthwhile strategy to offload all your cleans as quickly as possible to be sure you free up as much claim-space as you can before you die.
 * If the Mafia has two Janitors, or a Janitor and a Forger, it's usually worth cleaning or forging every person who dies, since you're unlikely to run out before the end of the game.
 * Retributionists are also unable to revive your cleaned targets. This can come in handy when dealing with a revealed Mayor, Jailor, or other important roles who often leave important Last Wills.
 * Even when you are cleaning roles that seem have no importance for the Mafia in their Last Will (such as Doctors, Witches, or Survivors), it still can be helpful to confuse the Townies in a situation where the role list is comparatively rigid (for example, Ranked Mode). This situation is more likely to be useful when you're likely to be lynched next day or the game would be likely to end because there is only few players left, and you would like to use all of your three cleanings.
 * If you're in doubt about when to use your cleanings, you may consider cleaning a person who is leaving the game or getting disconnected ("apparently committed suicide"). Those who left the game are incapable of telling a Medium their true role, and are usually not investigated and not watched by Lookouts (especially on Night 1), and they are guaranteed not to retaliate! (eg. Veteran and Werewolf). This always sheds doubt especially on semi-random role lists, as Townies will be unsure of the existence of that role.

Taking advantage of your cleanings

 * You know your target's role, so saying you are a Medium the next night and revealing their role, claiming they told it to you can support you. With this way, you can trick the Town by saying in the name of the dead people, for example, "The (name/role) says X is suspicious/Mafia/Neutral Killing." when X is not a part of the Mafia. Moreover, you can do other things to make you naturally believed as a Medium by becoming a messenger (i.e. if Jailor has executed a Townie, you can say "The jailed Townie is getting mad at the Jailor").
 * However, keep in mind that sometimes it's normal to have two or more Mediums, which would result to the real Medium calling you out as the dead people will alert the real Medium(s) during the night.
 * This strategy may have a backlash when you're standing out as a Medium for too long without the Mafia trying to kill you, especially when you have revealed a lot of "important" information publicly. The Townies might think you are a Janitor instead. Many Townies will rapidly lynch any Medium claims when it becomes clear there's an active Janitor.
 * Another option you can do is to pretend or role-play to be the role that you cleaned, especially because only you can read your target's Last Will. Many unique roles are rarely claimed due to the ease with which they can be counterclaimed; cleaning can open these up to the entire Mafia (although informing the Mafia of this risks alerting a Spy.) In all cases, be aware that this risks getting you exposed by a Medium and that these claims trust the Town to not dig any further and demand conformation going forwards; usually the Town won't ask for more confirmation once you're "confirmed", but it may happen if the game drags on or if something else calls attention to you. Regardless, when a cleaning allows them, some of the most powerful claims are ones that the Mafia is rarely able to make (and which therefore are less likely to face reflexive scrutiny):
 * While it's dangerous, claiming to be the Jailor is sometimes plausible after cleaning the real Jailor, as the Town will frequently not bother to ask for additional confirmation, trusting the real Jailor to sort you out if you lied (and are unaware that the real Jailor's dead); you can also use previous records of who the Jailor jailed from their Last Will in order to get them to "confirm" you as the Jailor.
 * After cleaning a Jailor, you can use other strategies that rely on the Town's assumption that the Jailor is still alive, too. For instance, your Godfather can claim to have been jailed as a way of explaining his Night Immunity, if called out by a Serial Killer or Vigilante.
 * Help your fellow members of the Mafia out! If a member of the Mafia is in trouble, tell a role of a person you cleaned so they can have claim-space. Of course, you won't be able to claim this role anymore, and it could get leaked to a Spy, but you could save another member of the Mafia's life.
 * Similarly, the Veteran is normally a dangerous role to claim because it's unique; but after you've cleaned one, it becomes incredibly easy and will discourage Investigators from investigating you in the future.
 * Transporter is usually an impossible role to claim due to the need to produce a Last Will that the people who have been transported can confirm. However, it sometimes becomes available if you steal the detailed Last Will of a Transporter; however, you need to claim said role quickly, as the Town may notice if "your" Last Will ends early. Alternatively, you can tack on entries at the end that transport you with members of the Mafia or with people who died; one or two Townies confirming the Last Will's transports will often be sufficient to let you pass as a Transporter.
 * In Ranked and other modes where roles are defined by general category, successfully cleaning a role opens up that entire category as a safe claim. For example, in Ranked, if the Doctor dies, it is usually safe to claim to be a Doctor or Bodyguard.
 * Giving the other members of the Mafia information based on your cleaning is valuable; but you have to weigh this against the risk of the information getting leaked to the Spy. If you do want to tell the Mafia the role of someone you just cleaned, it might help to just say that role and nothing else, so a Spy won't know if you're a Janitor reporting who you cleaned or a Consigliere reporting who you've investigated unless the Any slot has already been taken.
 * You are still powerful combined with a Disguiser. If you clean a unique role, the Disguiser can then disguise as that role. You can also find Neutral Killing roles based on what they claim, as you will know what is and isn't possible.

After Out of Cleanings
When out of cleanings, don't give up! You still contribute to the Mafia via voting, sharing out strategies in the Mafia night chat, or perhaps becoming a Mafioso later.
 * If you've already pretended to be as Medium (and you're safe that there are no actual Mediums left), you can continue the disguising strategy or simply saying nothing "as no Townies are talking".
 * If you have no cleanings left, it can be a good idea to try and take a hit for a more important member of the Mafia (Godfather, Janitor with cleanings left, etc.) Try pulling attention to yourself to draw it away from others. Only do this if it is clear that another member of the Mafia is in danger of getting enough suspicion on them, they are lynched or killed, or if they have a more important role in the Mafia than you do. Keep in mind you do not need to be alive to win when the Mafia kills everyone.