Do I need to install a sump pump?
It sure seems to me that a sump pump would be a good idea, especially if you don't want to keep drying it with a wet vac.  I am assuming the pit you speak of is of some solid material, not just a hole in the dirt?

A sump pump is pretty easy to install. A small one with a built in float connected to some tubing running out of the crawl space would do the trick.  You just need to supply some electricity, set the pump on the bottom of the pit, connect the hose/tubing and your basically done.  It will work automatically when the water raises the float.