Why won't my pressure washer mix in the detergent?

Using the wrong spray tip to apply detergent can prevent the detergent from mixing properly with the spray. Use the low-pressure spray tip (usually the black tip) when applying detergent. A clog in the detergent siphon tube can also inhibit proper detergent mixing. Check the siphon tube for a clog and clean the tube if necessary. If the siphon tube is clear, then you'll likely need to replace the chemical injection kit on your pressure washer.