Cleaning a strainer or sieve can be tricky, because food particles tend to lodge in the tiny holes. To avoid this, do the following:
Wash your strainer immediately, so that food particles don't solidify.
If solids do end up sticking, soak the strainer in hot, soapy water.
Scrub the strainer inside and out using a stiff-bristled brush.
If food particles persist, the strong pressure of a hand-held spray-hose attachment may help.