Be careful with using WVO in someone else's vehicle. You could be liable for any repairs they decide are necessary if they have any problems after your hire is complete, or you have during it.
the minimum would be:

• drain the tank and refill with new diesel
• purge all fuel lines
• replace all fuel filters
• overhaul injector pump
• replace injectors.

And they have the right to recover all of the cost AND any loss of income from hiring the vehicle due to the "damage" caused by you.

Please respect the property of others and use alternative fuels ONLY with their permission.

There is a time worn saying which is as relevant now as it was when transcribed in the bible 2000 odd years ago:
"do unto others what you would want them to do to you"



Regards,
Tony