Our house is 35 years old and still has its original septic system. The soil in the area of the leach bed is gravel and drainage has never been a problem. However, the system has backed up twice in the past 10 years. Each time we had the tank pumped, and the line from the tank to the distribution box snaked, which cleared up the problem each time. The snake he used each time was a manual snake that he simply pushed back and forth until the effluent started flowing again.
After the first backup, we started having the tank pumped every 2 years instead of 4-5 years. The last backup was 3 years ago, at which time we decided to have the tank pumped every 18 months. There have been no problems since.
The most recent pumping was a few weeks ago, and I had the chance to talk with the licensed plumber (restricted sewer) who did the pumping about the issues we've had. He explained that the concrete tank is still in good condition and the leech bed *seems* good based on (1) visually examining the vent pipe at the end of the bed, (2) being able to detect suction from the vent pipe when he put his pumping tube into the opening leading to the pipe out of the tank, and (3) the fact we have never had any sewer smell from the vent pipe. He suggested the following:
1. Replace the 4" cast iron pipe between the tank and the distribution box with 4" PVC. This is the pipe that has clogged twice. He's not sure how long it is, but guesses 10 to 20 feet.
2. Replace the U-shaped baffle (which is still in good condition) with a PVC Tee Baffle. He explained this would reduce the amount of solids leaving the tank.
He offered to do this for $300 plus pumping the tank again if we have the line exposed and accessible. I asked if it would be worth hiring someone to send a camera into the leech bed, and he said it would not be worth it, because it's a safe bet that underground cast iron this old is probably rusting closed and causing the blockages.
Does this seem to be a reasonable investment for a 35 year old system based on his assessment?