1. Put pot roast in a deep bowl. Sprinkle generously with salt. Pour vinegar and 1 cup boiling water over. Add onion, bay leaves, cloves, peppercorns and sugar. Cover and refrigerate for 24 to 36 hours, turning several times.
2. Remove meat, reserving marinade. Pat meat dry, and brown in hot fat in a large crockpot with browning unit or in skillet. Pour 1 cup marinade over meat in cooker. Cover and cook on low for 7 or 8 hours until meat is tender.
3. Strain juices and return to cooker. Turn control to high. Thicken gravy with gingersnap crumbs, stirring constantly.