The train, which can be identified as the Central line by its red bars, is seen drenched by urine in the disturbing video.
The caption warns commuters to “watch where you sit”, and is one of tens of videos shared to an account named “TheOriginalGangP*ssers”.
The video has been viewed over 700,000 times, and commenters are disgusted by the content.
One user vowed that they would “never” sit down again, with another saying they were “never taking the Central line”.
The TikTok channel, which has almost 19,000 followers and 810,000 likes, says: “Content is filmed mostly in toilets with permission. Footage is submitted by fans”.
Other videos on the account show people urinating on floors of toilets, on toilet paper, and on walls.
The profile picture, shows a cartoon caricature of a man with a creepy smile, with the words “GANG P*SS” in large letters, accompanied by an image of a toilet that has been crossed out with a red X.
Those who are caught urinating in public could be fined under the Public Order Act, or punished for indecent exposure.
Indecent exposure is a sexual offence, and can land those convicted in jail or on the sex offenders register.
Speaking to MyLondon, the account holder of “Gang P*ssers” said: “The toilet seat remains open but for now I’ll take a step back and continue my business on the floor.”
Express.co.uk have contacted TfL and TikTok for comment