Just because you've been in the construction trade trade for a lifetime doesn't mean you know it all. In fact in this situation he knew just enough to get someone killed, or sick at the very least!
There are several things about the way this clothes washer drain is plumbed that violate plumbing code; the most concerning of which is no p-trap. No p-trap means no means of preventing sewer gases from entering the residence. It's not just an odor problem, it's a life safety matter. The real problem doesn't have an odor, is highly combustible, and can cause death by Asphyxiation in high enough concentrations or heath effects with long term exposure in lower concentrations. Any guesses???? If you're thinking Methane you are correct. Methane gas is a byproduct of decomposing organic matter. This is one of the primary reasons for licensing requirements for plumbing contractors; understanding and managing the dangers and risks associated with human waste.
Do be a victim in your own home, call a professional plumber; even if it's just to make certain you (or that know it all handy person) has done it properly... It could save your life... Plumbers do it everyday.
Thanks for visiting,