The plumbing in my home seems to have a very "weird" venting scheme. There is one long waste pipe (in basement) and, as far as I can tell, fixtures are drained as follows: 1. sump pump up through check valve (washer drains into sump); 2. after several feet of pipe, kitchen sink (dishwasher drains into the kitchen sink drain also); 3. after a couple feet of pipe, a vent pipe connection; 4. after about another foot of pipe, ANOTHER vent pipe connection (why in the world would 2 vent pipe connections have been made next to each other?); 5. after a couple of feet of pipe, the bathroom sink; 6. after a couple of feet of pipe, the toilet; 7. after several feet of pipe, the bathtub. The waste pipe then extends about 12 more feet to the end of the basement, one 90 deg elbow down, one 90 degree elbow to the left, then about another 20 feet to the basement wall (cleanout before wall), then out to the septic tank (about another 12 feet).
I'm having problems with the toilet flushing and even being siphoned when the washer or dishwasher drains. Should the vent connections have been made differently? Could the vent system (only seems to be one stack out the roof) be clogged?