I use PH Neutral snow foam from
www.cleanyourcar.co.uk - their own brand - 6 squirts in the foaming lance, and rest toppped up with hot water and boom !!!! Its like my car's been resprayed in white ! leave it for 15mins, and then rinse, and results are good for loosening bird ****, and pulling off dried on dirt. Obviously fully washed after, but snow foam does work well on encapsulating the dirt and softening up tar, and birds sh*t.