Dryer venting is needed to carry moisture and warm air from your dryer to the outside. Without proper venting, both moisture and lint can build up in an enclosed space with a dryer, possibly creating a fire hazard. However, running a dryer vent to the outside, for example through a crawlspace, isn't difficult. Ductwork can be purchased in various lengths and fittings at your local hardware store, and fitting is done by means of tape.
Measure out the route for the dryer venting through the crawlspace. This will give you an idea of how much venting is needed.
Turn off the electrical supply for the dryer by unplugging it from the wall.
Find a location on the exterior of your ductwork. Hold the duct up against the wall and trace the outline on it with a pencil or marker. Drill a pilot hole with a power drill and drill bit. Cut out a circular hole with a jigsaw and appropriate cutting blade for the wall material. Sand down the edges with sandpaper.
Insert the exterior duct into the hole in the wall. Secure with screws.
Drill out any holes in walls or ceilings to access the crawlspace in the same manner as you did through the wall. Use a portion of the ductwork as a template when cutting the hole size. Sand down any rough edges with sandpaper.
Loosely fit together the ductwork between your dryer and the exterior duct.
Install a dryer booster fan in the crawlspace on long duct runs. The exact length of your duct before a fan must be installed will depend on your local building codes. Wire this fan into the electrical circuit. Install a switch near the dryer so you can control the dryer booster.
Connect the ductwork between the dryer and the exterior duct. Fit the duct pieces together. Secure each piece to the next by wrapping the connection with foil duct tape.
Although flexible ductwork may be easier to work with, it also traps more lint than smooth ductwork and requires more cleaning.