We installed a low-flow toilet about a year ago. After about 3 months we noticed that when the wash machine in the basement drained it would cause the water from the toilet bowl on the ground floor to gurgle, bubble up and drain out. This also happens when the bathtub on the upper floor is drained. Plunging the toilet seemed to help the first time for about 2-3 months. We are on a septic system.Any help?
I would check the vent on the plumbing, also it appears you have a stoppage in the drain. It appears when you have substantial flow the drain starts filling @ with no place for the air to release it raises the water in the bowl, when the water in the drain is being released through the drain slowly and no air being admitted through the vent your water leval would pull down. Check the vent, drain and your septic tank it could also be filling.