My house was built in 1930. We have 3 square drains (no metal fittings, just straight holes) in the basement. 2 drains lead into the third through ci pipes. Another c.I. pipe leads from the 3rd out to the public sewer. The pipe leading out the sewer is old.. somewhat corroded/irregular 3" diameter and horizontal. It either has no trap or a dysfunctional trap, because sewer gas comes through every now and again. During the fall it's the worst. We put water down the hole, which alleviates the problem temporarily. What's the fix for this?

Try pouring cooking oil or anti freeze down the traps. That will eliminate any evaporation that will allow smells to pass. Good luck. Tom