I just got a 2014 F150 that the previous owner liked to play in the mud. I have started cleaning the underneath of the truck. Inside the rockers appear to be packed with mud. What is the easiest way to remove this? Any help would be appreciated.

 

H2O (water) and lots of it. Lift and pressure washer.

As a pre-soak, when it's parked, consider putting a lawn sprinkler under it and letting it run for awhile.
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Yeah I have done the sprinkler method with my Jeep. The mud I have is inside the rocker. I am just flushing it with a hose and will follow up with compressed air for drying and coating with Fluid Film.

 

Patience and a good strong hose and/or pressure washer....

 

Agree on the lawn sprinkler. Let it run for a day or more. Stuff trapped behind a rocker panel might merit pulling fender liners out.