Yet another thread. I didn't see this resolved in any of the previous threads that I could find via search.

Here's the situation. New house. Electric water heaters. No flexible connections to hot water. copper pipe coming from heater, then PEX to the bathtub (deck mounted tub filler, Kohler). Doesn't come out when the cold water only is turned on. Just hot. there's quite a bit of sweated connections at the faucet, under the deck. My first thought was that it's excess flux coming out. Is there a way to check to see if that is what the stuff is? Some gets caught in the faucet aerator but most comes through and sticks to the bottom of the white cast iron tub. Very messy to clean. I haven't noticed the specks at any other sink or tub that these water heaters supply. Just this one faucet. As far as I know there's just copper and pex pipes involved.