Dumb mistake

I bought this: https://www.etrailer.com/Automotive-Tools/FloTool/FTF3NC.html?feed=npn&msclkid=c1cc4dee00ef1daf4df92c0da443aa20&utm_source=bing&utm_medium=cpc&utm_campaign=Bing%20%7C%20Shop%20-%20Automotive%20Tools&utm_term=4577404350181664&utm_content=30%20-%2060
Works well for my WET diesel fuel.

And I wouldn't worry about it. If you were driving, then the majority of the rain blew over the bed of the truck. The 10 drops that went in it will be caught by your water filter.

Bill

M.R.E. wrote:
I filled up my 5 gal can with diesei in back of pickup when towing and forgot to put cap on and drove for 3 hours in light rain. Will some water damage the fuel ? Is there something I could add to the fuel ?

Yes, through the 5 gal. can of diesel AWAY!!!!! Could cause real problems and cost you some $$$$.