Pull the dryer just forward enough for you to squeeze behind it to access the dryer vent. If the space is really tight, you might have to carefully climb on top of the washer and drop down into the space behind the dryer. Unplug the power cord and pull the existing vent away from the dryer, if it has one already attached. You may have to unscrew a band clamp to remove it depending on the type of vent. Pull the other end out from the wall and discard it, taking care to spill as little lint as possible.
Bend down and check the dryer exhaust outlet. If it is full of lint, use a hand-held battery-powered vacuum to clean it out. Use a flashlight to make sure you have removed all of the lint.
Fasten the periscope box vent to the dryer exhaust outlet. In limited space, you may have to ask a friend to tilt the dryer to allow you easier access. Slip a band clamp over the bottom of the periscope box, and then guide it onto the exhaust outlet so that the band covers both the outlet and the bottom of the periscope vent. If the wall vent is to one side of the dryer, rotate the periscope so that it lies horizontal to the floor in the direction of the vent. Otherwise, leave it in a vertical position. Tighten the band with a screwdriver until the connection is secure.
Lift and extend the periscope vent until it is the same height as the wall outlet. If the outlet is high on the wall or on the ceiling above the dryer, extend the periscope only until it protrudes a few inches above the back of the dryer. Then carefully push the dryer back against the wall. If the wall vent is directly behind the dryer, raise the periscope to the height of the vent, but do not move the dryer just yet. If the wall vent is to the side of the dryer, extend the periscope box vent a few inches past the side of the dyer. Do not move the dryer.
Slip a band clamp onto one end of a flex vent, and then attach the end of the vent to the unattached end of the periscope box vent. Tighten with a screwdriver until the connection is secure. Slip a band clamp onto the other end of the flex vent, and attach it to the wall outlet, again tightening the clamp until it is secure.
Gently push the dryer back against the wall, if you have not done so already.