Try flushing every drain point, sinks, showers, Laundry, toilets, outside, with a heap of water, and chemicals to if it will make you feel better, Drano worked for me in my old place.
I think there’s no P trap installed so no point of pouring in water and chemical.
Unless someone has built it super dodgy there most certainly would be one, if not near the inlet of the drain then certainly before the sewer big old cast iron thing, probably underground, if you live in town. if you’re brought an old farm house that old mate built himself then lord only knows
I am sure the previous owner got some dodgy plumber to save some money. He was an Italian guy and was living an awful life in that house. None of the windows worked , shitty paint etc. I am trying to fix all one by one. Also, I live in the city , its a duplex.
