Help .. oil field water truck job

I have a pretty decent job coming up. I’m offering a free truck cleaning yo get my feet wet on how to price this job. My issue is I’m having trouble finding a good chemical or detergent to use overall for the cleaning. If anyone has any experience with this the help would be appreciated. I dont want to dull the paint or polishishing but need to get the crud off. Thanks again

Call Hydro Chem in Grand Rapids MI

They are pricey but have good fleet line of chems. Sales reps are knowledgeable

Thanks much