You have a Poo pyramid. Most likely from using it with the valve open. Fill it to over half full, and let soak to soften and break up. Drive around awhile, curvy roads are best to slosh/agitate it around to break it up. Dump and repeat as needed. It may take several times to fully get it cleaned up. Filling it to about a 1/4-1/3, add a half of a small bottle of dawn to it, and dumping 20 pounds of ice in it, before driving it around will also help break it up. If it is pretty solid, a good soaking first will help greatly. When clean after dumping, put in at least 5 gallons of water with your treatment for best results. Never be stingy with the water when using either.