Ahead of its release on July 18, the makers of Saiju Kurup and Suresh Krishna's Flask dropped the film's trailer. It is written and directed by the National Award-winning filmmaker Rahul Riji Nair, who previously helmed films such as Ottamuri Velicham, Dakini, Kalla Nottam, Kho-Kho and Keedam.

The trailer of Flask begins with a shot of Saiju’s cop character holding a flask in confusion, accompanied by a voiceover stating that he has been posted as the Personal Security Officer (PSO) to a judge. The voiceover also mentions the competition for this PSO posting. This is followed by Saiju’s wife asking about the duty of a PSO, to which Saiju replies that it simply means being with the judge all the time. Saiju’s father jokingly adds that it basically amounts to being the judge’s wagging tail. We are then introduced to the judge, played by Suresh, who, judging by the build-up, appears to be quite an eccentric character. The trailer also shows that Saiju’s character has a fondness for singing, while another voiceover explains that the judge does not like music or singing. This is juxtaposed with visuals of Saiju carrying out his duties as the judge’s PSO. The narrative then shifts to a Maoist leader, played by Sidharth Bharathan, who has kidnapped both Saiju’s and Suresh’s characters. Brief glimpses follow of a shootout in the forest as part of a rescue operation to save the cop and the judge. Overall, the trailer promises a fun-filled comedy thriller centred on a cop and a judge.

Flask also features Aswathy Sreekanth, Balachandran Chullikkad and Zhinz Shan in prominent roles. On the technical front, the film has cinematography by Jayakrishnan Vijayan, editing by Christy Sebastian and music by Sidhartha Pradeep. It is backed by Rahul, Lijo Joseph, Rathish MM under the banner of First Print Studios, with Vineeth Venu, Jom Joy and Shinto KS serving as co-producers.