Since last week every time someone takes a bath the T&P valve
discharges a small amount of water. When this happens, the water looks
a bit rusty. If I pull lever on the valve, the rusty water will drain
and for a day or so there'll be no more leaks, then it starts again. I
checked the water line pressure and it's at 60 PSI.

I've replaced the valve and flushed the tank for about 30 min - two
days later the leak is back and water is rusty again when the lever is
pulled.
Any ideas?

thanks,
GE