I want to run a custom tool created with the Model Builder in ArcGIS. It needs to output to the SAME file each time it runs, just adding the data. Basically I have a custom Dissolve tool that will dissolve (in this case) counties together based on user selection. I need a single file containing ALL the dissolved final shapes, but the Model Builder complains unless each output file is unique. Is there anyway around this or do I have to create dissolve_1, dissolve_2, etc... (to 500 or so) and then combine them afterwards?