The condensate pipe just goes down into the drain opening. When a sewer backup occurs it will spill out onto your floor. It will not be sucked up into the equipment because you a P-trap with water in the elbow. Water prevents any suction.
Mine has been working this way for 25 years and no issues.
The trap stops flue gases from entering the drain pipe, and allows free flow, or stopping "water slugging". That's also why you have to trap a/c condensate with the evap coil on the negative side of the blower.
The trap is on the negative side of the blower. if the trap was not in place, the...
The P-trap with water in the trap prevents pulling the "sewer gas" from the drain when the blower is running. Just stick the pipe into the drain grate.