Funny. That might also explain partially why they are supporting Hillary. Sniffing gasoline is known to cause brain damage. But seriously, the perpetrators would have to use some type of funnel to hold the little spring door open at the top of the filler tube, so the bleach would make its way to the bottom of the tank almost immediately because laundry bleach is almost completely water which is heavier than gasoline.
I worked in hazmat for many years. Gasoline is so much more volatile than the little bit of chlorine that might escape from whatever tiny amount of residue might have been spilled, that it is completely implausible that anyone could detect bleach by sniffing a gas tank. The fact that they added this detail indicates that the entire story is made up.