Originally Posted by serapis
I heard washing up liquid damages the seals on the windows.
I just love the idea that washing up liquid will do more damage to a car than a commercial car wash. The reason why you shouldn't use washing up liquid is because IT WON'T break down heavy soiling.
Car wash detergents are designed specifically to break down traffic film, mostly diesel residue. They remove oils, waxes in a way that washing up liquid won't
Washing up liquid is by necessity relatively safe for contact with human skin. It is hardly likely to be capable of disolving your car or its paint.