My question refers to the whole house trap.
Is the trap really necessary to have. I am replacing a broken laundry room floor drain and in order to do it right (get a clean cut) I decided to expose the waste pipe (pvc) outside the foundation wall. My father in-law arrived and explained that I needed to add a house trap since there is only a straight 4 inch pipe leaving the house with cleanouts( 1 on both ends vented every 50 ft) I guess it makes sense if the floor drain would dry out. would it be necessary if I didnt have a floor drain at all?

a lil bit of knowledge can ....