Five years ago a contractor connected my irrigation system to the potable water line to my house. This water source is only used maybe twice a year when my secondary irrigation water is not available. The connection consisted of a T on my main line, a 3/4" x 10" black iron pipe, connected to a 1" brass stop and waste valve, connected to a 1" iron elbow, which connects to the irrigation system (almost entirely PVC). Recently when I was irrigating with the potable source, water started coming up above ground and flooding my front yard. I shut off the stop and waste, the dug down 4 feet to find the problem. The elbow coming out of the stop and waste had a hole in it. There was a flat spot on the elbow as if it had been flattened on a grinder. The center of the flat spot was very thin. It had rusted through in that spot from the outside. The entire outside of the elbow is very rusty. The inside looks OK. I am going to replace the elbow with a PVC elbow. I'm wondering if I should replace the 10" piece of 3/4" pipe that connects the stop and waste to the potable water line. The pipe looks ok on the outside, no rust. I had to dig a huge hole to access these pipes. I don't want to dig this hole again. I don't have a way to shut off the water at the street, so I would have to hire a plumber to replace that short black iron pipe. Is it worth replacing that pipe with a 1" copper pipe, or should I just leave well enough alone?