Who knows what technological marvels await in the city sewers.
Search the sewers is a mission in Ratchet & Clank (2016 game) taking place in Blackwater City on planet Rilgar. Ratchet and Clank searched here to find look for equipment. They eventually found a button that caused the sewers to overflow.
This is a mandatory mission, and involves little combat. From the ship's starting point, travel left to the metallic bridge and use the Swingshot to latch onto a versa-target over to a small raft, then use the next versa-target to reach a sewer pipe. Travel down the elevator inside here and in front of you is a pool with deadly sharkigators. Use the Hydrodisplacer on the plug by pressing next to it to drain this pool, then kill the prone sharkigators with the OmniWrench and travel up the wall to the next spot. This contains an empty wall in front of you, and using the water from the previous plug, attach the Hydrodisplacer and fill the water in front, allowing you swim up to a tunnel.
Smash the barriers in the tunnel here to come out on the other side. Here reveals another pool with a sharkigator, so plug the Hydrodisplacer to drain the pool, jump down and kill it, then travel through the tunnel and destroy the barrier. Head back up to the Hydrodisplacer plug with the ladder, and fill the water back up, then jump down and swim through the tunnel. Up in the next area, destroy the crates for bolts, then slide down the sewer pipe to a small, dead-end room. Hitting the green button opens the door in front of you and commences the mission "Escape the sewers!".