Well, deep dive and one will see what the difference is. Diesel is combustible. Throw a match in it and the match will go out. Gasoline is a Flammable, toss a match at it and it explodes.
A tank rated for combustibles have simple vent systems since Diesel doesn't evaporate like Gasoline does, especially in hot weather. The tank rated Combustible only will vent the fumes creating an explosion hazard, and therefore are illegal to store gasoline in. It must be UL listed in order to carry class 3 fuels.
Thats the simple part. The complex part is now in transporting such fuels. There are rules from the FMCSA that restrict how much fuel of a certain type can be transported without requiring hazmat endorsements and placards, as well as the type of containers used to transport the fuels.
Then there are Federal DOT and State DOT regulations that must be met.
There is only one company that sells bulk transfer tanks for Gasoline, and that is TransferFlow as they are the only ones with the proper certifications to meet all the regulations.
Diesel is limited to 119 gallons before meeting restrictions, so the 50 gallon tanks, as long as they have the flammable label on them, are fine to load up and fill.
According to the regs you are only allowed to transport 8 gallons of gasoline, but there are conflicting regs from states. in NY you are allowed to carry up to 4 five gallon containers of gas. Pretty sure that is the norm in all states too.
Then there are OSHA requirements too.
There are also USDA requirements,
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjgjfPPiKH4AhUZX80KHXSrByQQFnoECAUQAQ&url=https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_043004.pdf&usg=AOvVaw3luoqN_L4oRbNIHajQKfW7
There is also a federal law that requires portable gas cans to have flashback safety devices installed.
I have one of those 30 gallon on wheels tanks, but it is no UL approved as far as I can tell, nor are the ones like it sold on Amazon and elsewhere. According to what I have read so far, it is not legal for me to strap it to my trailer and take to the gas station to fill it.