In most plants, the separation is done using human sorters but, in newer plants, there are infrared sensors that identify the plastics based on the spectrum of light they reflect.
These first human sorters search for large items that shouldn't be there and might slow down the machines, such as clothes or towels, which can get tangled up.
After I heard about it, I sorter oozed around the barrooms pickin' up gossip and I found out that somebody wants to buy in Tara cheap at the sheriff's sale, if you can't pay the extra taxes.