I try just water with a little soap....for several days...
But I hope what you are seeing isn't rust....
Linda C

What is it made out of? Is it stainless or aluminium?

Dissolve some dishwasher detergent in a sink full of water and soak the chinois overnight. Or maybe you could put a cup of ammonia in a plastic bag and put the Chinois in the bag and seal. Leave for a number of hours or overnight. Should soften up the food enough to wash off. Both these methods work in cleaning the racks in the oven so I'm just guessing they would work on the Chinois.

Ann

stainless....i think...

If it's stainless you should be able to soak it and soften the goo and then scrub with a toothbrush....and it should come clean.
But there is always the chance that the previous owner used it for something like straining paint!
Linda C

If it is stainless, try putting it through a dishwashing cycle.