You may use following steps for this purpose:
1. Create input file using normal procedure (standard program template, etc.), for one of the your tanks.
2. Open text file (with .$2k extension, most probably. May be easily recognized on opening, as it will be containing joint & member numbers, loading etc) of your model in Notepad (or some other text editor), and make changes in loading & other required parameters, for your next tank.
3. Save the amended text file with a new name, as 'all files' with the same file extension, as that of original text file.
4. Import the newly created text file in SAP2000 and save it as a new SAP2000 database file.
5. Repeat steps 2-5 above, for all the remaining models.
HTH
A good structural engineer is often a blessing for others.