Place your trash can in an area that it can get wet.
Squirt a bit of dish soap in it.
Use a sprayer attached to a hose and spray that trash can down!
Empty the water.
Repeat if necessary.
May also clean with bleach after the soap.
It will suds up heavily, but the heavy sprayer will almost always work to remove all of the grime on the sides and bottom. Only in extreme cases will you need to use a pressure washer or get a scrub brush to manually clean the garbage can.
You can get a sparkling clean, almost new garbage can while barely touching the trash can itself.
Every family is different, but it should be sufficient to clean your outdoor garbage can seasonally.