Make sure your drysuit is bone-dry before you test it. Test on a dry, clean surface, too. Turn your drysuit inside out, and use taper plugs (or some other objects of a similar size to your wrists, ankles, and neck) to fully seal the suit. Pull the drysuit closed (from the inside), and insert a hose through the neck seal to fill with water. Make sure all of the seals and gaskets are fully taped off before you fill. While the suit is filling, look around for any hints of damp or water leakage. If you find any leaks, use a marker or a bar of soap to mark the spot. Repeat until you’re certain A) the suit doesn’t leak, or B) you’ve identified all the leaks. Empty the suit, dry thoroughly, and use Aquaseal or Seal Grip to repair any leaks.