He will send you to recover 5 rotten fish barrels to feed the Leviathan. They are small, randomly-spawning, harvestable buckets found in Jarsath Wastes around the rivermouth at ( 611, -43, 1213 ) /waypoint 611, -42.74, 1213.
Head to Chelsith and speak with Uguaz Tysk ( -9, 5, 398 ) /waypoint -9, 5, 398 at the beginning of the zone. (You need to speak Goblish.)(VERY IMPORTANT NOTE: Don't kill Mucus of the Deep one yet. Otherwise you'll have to wait for the timer to expire (90 min) and zone into a new instance to kill Mucus for the next step after destroying the idols!!!) You can swim around him, or grey him out.
You must destroy 4 idols. These large idols are found at the Upper Level(s) Named Yah-lei spawn areas and look like statues of Frogs, tentacles, etc. Try in front or behind or move around the altars until you see text announcing the idol, then activate the rock crusher. You must have the rock crusher EQUIPPED (charm slot, manually equipped) in order to use it.
Idol of Obedience ( -344, 35, -280 ) /waypoint -344, 35, -280. Guarded by Bbal'Gaz
Idol of Dominion ( -130, 38, 351 ) /waypoint -130, 38, 351. Guarded by Krel'Vhap
Idol of Sustenance ( 394, 48, -215 ) /waypoint 394, 48, -215. Guarded by Gok'Chai
Idol of Exaltation ( -2, 35, -403 ) /waypoint -2, 35, -403. Guarded by Kuom'Ziki
Place the 5 Barrel of Rotten Fish around the Feeding Chamber (the first ring pool to the left when entering Chelsith). Stand on the edge of the pool (out of the water) and use the bucket FYI: You can place one bucket for update then pick it back up and put it back down for another update until you have all 5.