A device used to manage the movement of surface water into and out of an attenuation facility. Drainage which runs through pipework installed to a fall, and not therefore under pressure. Water that is below the surface of ground in the saturation zone. Will not allow water to pass though it.
Examine your crawlspace from both the inside and outside and find all holes and entrances into the space. If your crawlspace is reasonably dark, going inside, turning off the light and looking for sunlight coming in from outside is a great way to do this. Seal the holes with expanding foam or caulk.
Unvented crawl spaces are permitted by building codes. In most areas of the U.S., sealed crawl spaces work much better than vented crawl spaces. Most building codes permit the construction of unvented crawl spaces. In the 2006 International Residential Code, requirements for unvented crawl spaces can be found in Section R408.3.