First, the land we live on is all clay and very little top soil. When we get a lot of rain nothing drains very quickly. So we have to manage how we flush during the wet seasons. I know there's not much I can do with that. Anyway; here's the problem I have. I have a two story home and have two bathrooms with one on each floor. when the toilet up stairs is flushed especially when it's wet, it gurgles back up in the toilet down stairs. I need to know if the toilet down stairs needs to be vented above the toilet dain line up stairs to fix this problem.