SPOILER WARNING: This article contains major spoilers for "Elseworlds, Part 1," the first installment of this year's Arrowverse crossover.
"Elseworlds," this year's three-show Arrowverse crossover, just answered a series-long Flash question: does the Pipeline have toilets for its prisoners? As a matter of fact, it does.
When Barry and Oliver woke up in the middle of each other's lives, they immediately tried to convince Team Flash of their true identities. Naturally, this plan failed miserably. Convinced they were crazy and that they may pose a danger to themselves or others, Team Flash knocked them out and locked them up together in the Pipeline.
The Pipeline is, of course, Team Flash's makeshift prison for Central City's most dangerous metahumans. Built out of the remains of the particle accelerator, it resides in the bowels of STAR Labs and features effective power dampeners. Additionally, each cell has a glass front door, allowing easy visibility for those on the outside. Noticeably, none of these cells have a visible toilet, which has left fans wondering for years where the prisoners went to the bathroom during their stay.
In "Elseworlds, Part 1," Barry answered that question. After Barry confirmed the Pipeline is indeed a prison, Oliver demanded to know where the toilets were. In response, Barry kicked a section of the wall. At that, the cell paneling slid back and a toilet emerged.
Oliver wasn't just asking to satisfy his own curiosity. He soon put together a plan, wherein Barry slipped off his handcuffs using Oliver's training and retooled the electrical panel above the toilet, then dropped the wires into the toilet water. This shorted out the power dampeners in the cell, allowing Oliver to phase through the handcuffs. Once he mastered the art of phasing, he grabbed Barry and phased them out of the cell. From there, they were able to breach over to Supergirl's Earth-38, where they adjusted to each other's skill sets and got their bearings.
This year's Arrowverse crossover event will involve the casts of Supergirl, Arrow, and The Flash. The event will unfold over three nights, starting with a special episode of The Flash on Sunday December 9 at 8 pm ET/PT. Then, it continues Monday, December 10, with Arrow, and concludes on Tuesday, December 11, with Supergirl.