Officers detained a 56-year-old Mexican citizen waiting to cross the border after they found marijuana in his commercial bus, according to NBC San Diego.
An border agent noticed something unusual and brought a drug dog to investigate the van, which was in line at the San Ysidro port of entry.
The dog reacted to the drug content, so the bus was scanned with an imaging system and it was determined that something was amiss around the gas tank.
The man had more than half a ton of pot inside the gas tank -- a street value, NBC reported, of $482,000. The 1,071 pounds were divided into 110 packets and stored inside the tank.