Toni tells Claude that he wants him to destroy two vans used by Mr. Wong's Laundromat, after the Triads had attempted to ambush him before. Toni tells Claude to drop by 8-Ball'sEightballs Autoyard in Saint Mark's to collect some grenades. After leaving Toni, Claude locates and destroys the three vans (two vans in the 10th Anniversary Edition), avoiding pursuing Triads after destroying the first van.
After the introduction cutscene, the vans are located in the heart of Chinatown and begin to branch out to other parts in Portland. It is recommended to drive there quickly because there is a possibility that the vans could intersect paths at one point, making it quicker to finish the mission.
Using the grenades is probably not the best way to destroy the van, as it will attain the player's wanted level if there are NPCs or other vehicles in the vicinity of the laundry vans.
It is possible to get the grenades and hijack the vans and push them into the ocean or drive them to the car crusher. The player will receive both money and the unused grenades.