My septic sys. Failed. Had a new one installed. Only thing not replaced, 15 feet of clay pipe under stone deck. When installed this section of pipe was found to be plugged up, a plumber came in and snaked the pipe, and freed the clog, now the waste water was going to septic tank. After they left I poured 25 gallons of boiling water down the drain in case of grease per the plumber. So now when flushing upstairs toilet the lower sink gurgles and the lower toilet bubbles. When flushing the lower toilet the lower sink gurgles and the toilet does not flush correctly, slow to drain but the waste product does go down. Yesterday I put a water hose in two vent pipes that are above these bathrooms. One was a 3" vent pipe the other was a 2" vent pipe. I let the water go in each pipe for several minutes with no visible effect. Afterwards I checked the lower bath and gurgling and bubbling were the same. In the upstairs bath a very small amount of black dirt was on the sink drain. I have not had any backups with waste water and it appears to be taking all the waste water that I can give it. Any ideas?