Two sisters and their cleaning-obsessed mother are at first only mildly annoyed by their drains being clogged. Until the drains begin to leak a foul smell and moaning.
While walking home from school Shimizu Reina is bothered by an acquaintance by the name of Kari, who is a sweaty, smelly, disgusting guy that Reina wants nothing to do with. She flat out refuses and runs home when he asks her to be his girlfriend.
Reina and her sister Shinri arrive home to their neat-freak mother scolding their maid for not cleaning hard enough. While washing up Shinri tells Reina to bring Kari to their home for a day in the hopes that their mother will scare him off for good with her obsessive need for cleanliness. Reina is still reluctant.
In the next scene a plumber visits in order to unclog some pipes. Their mother repeatedly scolds him for his dirty socks, dripping pipe water on the floor, and dropping what was stuck in the pipe on the shower floor. It is made clear just how obsessive their mother is. She's a recluse, divorced with no real communication with the "unhygienic majority".
The next day Reina takes the long way home from school and encounters her father on the way. He invites her to have a cup of coffee with him which she declines to head home. It's Shinri this time that encounters Kari, and she invites him over to meet her mother. Shinri and Reina's mother appears at the window shouting at him throwing eggs. Shinri joins her and he leaves, defeated.
When Reina returns she scolds Shinri for her actions, worried that Kari might come back for revenge since he knows where they live. Shinri reassures her that everything is fine and their mother would keep him away. Sometime in the night a person slips in through a window. Their mother is there immediately and attacks the intruder with a baseball bat. Reina and Shinri are woken by the commotion and turn on the light to reveal that the intruder was their father, whose body lay on the floor in a pool of blood. Their mother tells the police it was self defense and her obsession with cleanliness turns towards the blood stains on the floor which just won't come off. When the maid insists that she has done all that she can and is scolded harshly, she quits.
More drains in the house begin to clog. While their mother washes her hands in the sink the water begins to back up. However then it starts draining, making an unusual sound. Instead of calling a plumber again, their mother tries using boiling water to clear the blockage. When she pours it down the drain the noise happens again, more intensely like screaming, and the drains remain clogged. Soon the moaning begins to happen regularly. Reina tries to believe that it's just the sound of water moving through the pipes, but Shinri insists that it is the sound of someone moaning. She says that it must be the voice of their deceased father.
Meanwhile their mother is obsessed with attempting to scrub the blood stains off the floor to no avail. She sees her hands covered in blood and runs to the bathroom, where a sticky hand reaches up from the clogged sink and grabs her arm. They find their mother panicking on the floor because her arm is dirty and sticky.
They call the plumber again, who this time declines to work in their house because of the mother's attitude. Their mother still sits in the bathroom with a bucket of water trying to scrub the sticky substance off her arm, but only succeeds in scrubbing the very skin off her body. Suddenly a foul stench begins coming from the clogged drains, wafting around the house. Shinri says that it's familiar- that it's the stench of Kari's body odor. Reina bursts into laughter at the absurdity in her sister's words when Shinri says that Kari must be hiding in the drain pipes. Only an arm can fit into them, never an entire body, she says. But Shinri is convinced, saying she heard a story about a boy who dislocated his shoulders to fit into a drain to be with his crush. Reina is the voice of reason, saying that he'd have to do more than just dislocate his shoulders. He'd have to crush his skull and the rest of his body to fit, and the smell is just that of hair and oil that has been sitting. She tells Shinri to go take a shower and calm herself.
But while Shinri is in the shower, she begins to hear the "moaning" again, and the drain cover shifts on its own. She panics, running to Reina saying that it really is Kari in the drains. Reina comes to inspect it, still not convinced. When the water recedes Reina feels convinced, but Shinri thinks it's possible that Kari is drinking their dirty water and excreting it out into their drains. They get into a fight, Reina blaming Shinri for leading him to their home, and Shinri saying that it was Reina's crush and not her fault. To prove her point Reina grabs her sister's arm and shoves it into the shower drain, telling her to pull him out if she's in there.
Shinri does feel something moving, and her entire arm is pulled in. Reina sits in quiet disbelief while her sister is pulled further in. Unable to accept it, Reina tells Shinri to stop messing around and walks away while her sister screams for help. Reina sits in her room, hearing the strange noise from the drain and her sister's groans of agony. Finally she decides to go check up on her again. When she walks in, all that's left of Shinri are her calves and feet sticking up from the drain, which are quickly pulled in as she disappears entirely. Reina panics and flees, admitting that her sister was right, and realizing that there were now two bodies stuck in her drains.