Softscrub
When I put my boat in the water, I topped up the tank with 5 gallons of diesel, it only needed about 3 gallons

So I wiped it up, but there ended up with some minor staining.I used softscrub (as mentioned on this site a couple of years ago) and it worked wonders.I didn't scrub hard and it took a couple of applications, but it got rid of it all.Hope that helps.Bruce.Neon Moon