What would be the best solution to use to maintain keeping roots out of the drain? Copper sulfate or something else? Rodded out the 4" cast pipe in June. Got a crapload (pun intended) of roots out. It's blocking up again. This is at our summer home and not sure if the lack of using the plumbing has anything to do with it or the unusually dry summer combined with sandy dirt. It's clogged up again. As far as I know, it's 4" cast until it meets with pvc the city installed maybe 10 years ago.