Unless you are seeing and hearing gurgling in your drains, it is probably not the vent. As stated, check for traps that may be dried out. Also check around the base of toilets for a broken wax seal that is allowing water to leak.
If you have never made a mistake, you haven't done much.
Without more info these are the only things that come to mind:
1. Don't allow pets in the house.
2. Clean up the mess the pets made when they were allowed in the house.
3. Flush the toilets after use.
4. Stop eating gaseous foods.
5. Put soiled diapers into a container outside the house.