Honestly, I’ve tried copper sulfate a few times and it’s just that—a band-aid. It’ll clear things up for a bit, but those roots are stubborn and always seem to come back. If you’re dealing with repeat offenders, root barriers or even pipe lining might be a better long-term move. The quick fixes just delay the inevitable in my experience.
I get where you’re coming from, but I’m always a bit wary about digging around pipes or installing barriers myself. Sometimes those “permanent” fixes can do more harm than good if you’re not careful. Copper sulfate isn’t perfect, but at least it’s low risk if you follow the directions. I’d rather play it safe than accidentally crack something underground… had a neighbor do that once, and it turned into a real mess.