A friend asked this question but I am not sure of the answer maybe someone on here can answer it

A gas can was used once or twice to carry diesel fuel and has not been used in about 8 or 9 months since

Now he wants to use the can to transport gas for his car

Is this safe to put regular unleaded fuel in the can as it did have diesel before
Is there something that he can do to CLEAN it,

Pour 1 pint of new gas into the container, slosh it around, and dump it with your waste oil.
If you have an old mower, use it for that. Then go use the container for gas.

The small amount of residual diesel will not affect the vehicle in question, use it.

I wouldn't mix any amount of diesel fuel with a gasoline motor.