Septic system question

Do those pipes go into the tank? I can't imagine what else they would be except tank access ports - but only you would know for sure. If they end at ground level they probably wouldn't be hurt by extending but I'd ask a plumber first. The septic system is NOT something you want to break.

Sewer drain cleanouts. One will angle back towards the house and the other will angle towards the tank/street. It will cause no harm to extend them, but probably is not necessary if under the surface for a few inches. Any decent plumber will find them with a rod. Bob

A well designed system has a vent, my honey dipper told me on his annual visit about 3 years that part of the problem was that mine was installed with no vent, and it has to have air to ferment. I put it back together with a stack and made a flowerbed around it, haven't seen him since, I miss him, but don't miss the back ups and expense. Likely the tubes are vents and clean-outs, no rocket science here, make them as tall as you like, use standard PVC tubing and couplers and glue. He may curse you if you make the clean-out too tall, but it can always be trimmed later. I used a 20 galon PVC drum I got from a car-wash service guy and cut to to fit & made a removable lid from the bottom of the drum. this made so the clean-out lid could just lift through the opening and nothing seals well enough to exclude air.