I just moved into a new house. At the back of the drain field (in the middle of by back yard) is a PVC pipe sticking up 12-18" out of the ground. I'm assuming this is a vent. My question, can I cut the vent to have it flush with the ground or a little below grade? I also have a vent right around the tank (or it might be a clean-out). Can this one be lowered?