Please help! My husband & I bought a house in Feb of this year. Shortly after we moved in, we started to smell a sewer smell (we have a septic tank but came from a house having city sewage)so thinking maybe the septic needed pumped, we had a septic tank truck come to pump but the man said our tank was nowhere near full. We continued to have the smell and had our basement waterproofed thinking that it might be the cause of our sour smell. This made some difference but we still have the smell. There is a drain in the basement behind the washer and dryer that if we pour water into, the smell gets better but we have been doing this everyday after we get a shower and I feel there must be something better to fix the smelly problem. When our furnace or air conditioner runs, the smell goes through out the house. What is the drain in the floor for anyways and can't we just seal it off? Will this create pressure and cause more problems or damage something? Where is this smell coming from? Please help!