Despite a recent campaign to raise awareness of the issue, some people are still putting in things like food waste and dirty nappies, contaminating whole truckloads of recycling - when these things are put into recycling bins in black or coloured sacks they’re not spotted until it’s too late.
If there’s a sack in a recycling bin and the waste crews can’t see what’s in it, they’ll have to assume it contains contamination and won’t empty it.