"sand' in toilet bowl
#1

I have what appears to be grains of sand in my toilet bowl even though I clean it every day. This problem started one year ago. I have cleaned out the tank and periodically drain the water in the bowel and scrub that out. The "sand" has etched marks in the bowl and it now looks dirty even after I have just cleaned it. Aside from the appearance, I am concerned that my pipes might be falling apart (the house is 66 years old) and causing this problem. Any suggestions?