Pigs are exceptionally clean. The misconception of them being dirty comes from a misinterpretation of their evolutionary adaptation. Unlike humans, pigs have very few eccrine sweat glands over their bodies. So they can't sweat out internal heat as we do. To make matters worse, domestically bred pigs have thicker layers of subcutaneous fat, which heats their core even more. Wild pigs have evolved a way out --> wallowing in clean mud. The mud coating keeps them cool through evaporative cooling. It also protects their hairless skin from UV damage and parasite attack. This urge to cool down in mud is hardwired in a pig's instinct. The problem arises in industrial settings where proper wallowing facilities are not provided & pigs are crammed in closed pigsties. To cool themselves down, they resort to covering themselves in their own waste. If given clean wallowing facilities, pigs are conscious enough to keep their latrine and living areas completely separate. The problem exists because we don't understand their biological and evolutionary needs.