With Sollozzo's drug warehouse and fronts destroyed, the narcotics business has been pushed out onto the streets. Break up a street market where drugs are being peddled, but keep an eye out for Tattaglia loyalists.
Reward: +5,000 Respect
Go to the market. You will see a blue marker above each pair of wooden food carts that you must destroy. The tommy gun is probably the best weapon for this. Take it out, go into free-aim mode, and shoot the carts. Don't bother destroying the carts completely, you just need to shoot them until they show the first signs of physical damage. Once the carts are taken care of, you need to blow up the smuggling truck which is in an alley across the street. Watch out though, there will be about three Tattaglias that will come after you to defend it. Mow them down with the tommy gun.
Then shoot the explosive barrel next to the truck, or just shoot the truck itself until it starts burning. Get to a safe distance and wait for it to blow up.