Cleaning under seat area

I took off my seat the other day. To clean off my bike after a muddy ride i did the other day and found tons of sand and dirt under the seat! Some its all over the place even down under the Flapper Valve! what is the easiest way to clean the under seat area? and how did it all get under my seat? any help will be appreciated.

Thanks Jake

Time to get out the Shop Vac. Sand will find its way into the smallest crevice on your bike. Rule one: If you get home and find sand in you shorts your bike needs special care too. Rule two: Don't hose the mud off your bike with the motor running.