The series follows the residents of Sinkhill, a 'forgotten East End district of a warped funhouse mirror vision of Glasgow, Scotland'; a place where crooks, deviants and killers as well as the ordinary folk unfortunate enough to live among them reside.
Sink contains examples of:
- All Just a Dream: #2 has Sharon hired to dispose of a dead body only to discover that the victim is still alive. She gives him her savings so that he can leave Sink and start a new life. Then it's revealed that he was Dead All Along and that she only imagined him being alive before proceeding to dispose of his corpse.
- Animal Motifs: Mr. Dig wears a fox mask.
- Affably Evil: Si McKirdie runs most of the organized crime in Sinkhill but can be fairly charming and easygoing as long as you're on his good side.
- Anti-Hero: Mr. Dig is a brutal vigilante who enjoys torturing criminals and beating them to death with his shovel.
- Badass Normal: Mr. Dig is just a guy with a shovel who happens to be a Peshmerga veteran.
- Baddie Flattery: Emma's not afraid to talk frankly to Si McKirdie, calling him out on the hypocrisy of making money off dogfights while claiming to like dogs. He genuinely admires this, noting that she's tough as nails, and tells her not to let the world change her.
- Bald of Evil: Si McKirdie, the kingpin of Sinkhill.
- Beauty Is Never Tarnished: Averted with Charlotte in #6; the clowns give her a Glasgow Grin as well as a clown nose that is forced onto her with needles on the inside.
- Cleanup Crew: Sharon is a cleaner in Sinkhill hired by people to get rid of bodies.
- Clownification: Those caught by the gang of Monster Clowns are given Glasgow Grins, have red noses attached to their faces via spikes on the inside, and are sprayed with some sort of insanity-inducing gas, after which they are inducted into the group.
- Death Glare: If Si McKirdie takes off his sunglasses, it's too late for you.
- The Dreaded: "Rab" Kilcolm was this back in the day, and when people recognize Florence for who she used to be, it comes back in full force.
- Driven to Madness: The clowns spray some sort of gas on their victims to drive them insane and induct them into their group. One woman manages to escape this ritual but is implied to have been driven insane from the experience nonetheless.
- Facial Horror: The clowns have hideous Glasgow Grins as well as red noses that are attached to their faces via spikes on the inside.
- Forced to Watch: As a lesson about the cost of change and what it means to ask someone like McKirdie for help, the crime lord forces Emma to watch as a number of fighting dogs tear apart the guy running dogfights in Sinkhill.
- Gang of Hats: Members of the "Dickheads" gang wear stretched-out condoms on their head. They're apparently supposed to keep them on 24/7 as well.
- He Who Fights Monsters: Mr. Dig admonishes a kid who wants to be a vigilante like him by telling him that killing changes a person and spoils them inside.
- Hope Spot: At the end of issue #4, Craig reflects on how his harrowing experience has made him a braver person, with nothing to fear anymore... and then an extremely familiar blue van appears behind him.
- If You're So Evil, Eat This Kitten!: Part of the initiation process to rise up in McKirdie's gangs is to commit an awful act or crime.
- I Gave My Word: Si McKirdie agrees to help Emma look for her dog at his fighting ring; when it turns out that the pup is already dead, he shuts down the dogfighting racket in Sinkhill, period, and has the guy running the ring killed when he protests.
- Made of Iron: In his debut, Mr. Dig takes a knife to the back and keeps on going. The hits keep comin' in later issues, as well.
- Monster Clown: A blue van filled with psychotic clowns drives around at night. Those unfortunate enough to be caught by them are mutilated, driven insane and turned into clowns as well.
- murder.com: Graphite Green is presented as an experimental rent-free luxury apartment complex in Sinkhill. In reality it's a false front for an elite televised competition for four killers to kill the most people.
- Paint the Town Red: It's very common for entire rooms to be covered in blood after people are killed.
- Pet the Dog: A literal example with McKirdie. After a young girl's dog is killed for 'bait' as part of a dog-fighting ring, he breaks up the operation and gives her an abused fighting dog to look after.
- Shovel Strike: Mr. Dig's weapon of choice is a shovel.
- Sudden Downer Ending: #7 is mostly played as a screwball comedy up until the ending, when the protagonist comes across an abandoned bus functioning as a death trap set up by a serial killer.
- That Man Is Dead: Florence Kilcolm feels this way about "Rab" Kilcolm, having chosen to leave her violent life as the wrong gender behind her. She briefly picks the "violent life" part back up to avenge an old friend.
- Vigilante Man: Mr. Dig is a fox-masked vigilante who dishes out his own brand of justice on those unfortunate to cross him.
- Wham Episode: The Graphite Green saga is the series' first two-parter and features Mr. Dig going up against four professional killers.
- Wretched Hive: The titular Sinkhill is this on its good days.
- You Can't Go Home Again: Not after stapling your Glasgow Grin shut, tearing most of your nose off, and killing several of the people who did it to you.
