bcollie,
I wouldn't worry if you have a small tank. Mine is 125 gallons, so i was dumping on average 20 gallons a week of salt water. Also after I dug it all up, I found the pipe was plugged were it led into a very poorly installed field. After talking to some specialist they all said to not let saline solutions from water softeners or fish tanks enter the system. The only concern I would be worried about is if your field area is a heavy clay based soil. The clay breaks down when the salt hits it and causes it to migrate much faster horizontally. It slowly fills in all the voids the gravel provides, and then the water in the system backs up into your house. If your field has a soil seperating fabric around it you should be set, but very few contractors get that detailed. Also I would have your tank pumped every 3 years at least, and at the first sign of trouble, saturated sewage smelling lawn, water backing up into the house, call somebody fast. Is also a good idea to know were your field and tank are and check those areas every now and then.
CG