All general-purpose washers have detergent attachments. Electric models usually have internal reservoirs, while gas models generally have siphon tubes that you insert directly into a container of detergent. As the detergent is pulled through the system, it mixes with water to make an approximately 12 percent solution, suitable for most applications. Because detergent needs extended contact to work effectively, it can be applied only when the machine is in its low-pressure mode. High pressure would blast it off as fast as it was blown on.
Detergents can pose a problem, however, especially if they contain bleach.
Houses are surrounded by grass and landscape plantings, which can be damaged by such chemicals. Root systems can actually survive quite a bit, but foliage is another story. To prevent leaf damage, choose a general-purpose cleaner that does not contain bleach. Thoroughly wet any plants you can't cover with plastic. Of course, if your siding is only a little dusty, it may not need a detergent.