The water heater is an 80 gallon Rheem Hybrid Heat Pump device. The waste line that is directly above the water heater is a 3” Schedule 40 pipe that feeds into a 4” Schedule pipe that goes to the septic system.
The place where the pump enters the waste line would need to have a trap and a vent just like any other fixture. Seems like a lot of effort for a condensation line.
An easier, maybe ugly way to do this would be to pump into the open side of an existing fixture (toilet or sink) in the level above.
An even easier approach would be to pump to the outside. Obviously if there is an existing nearby sump pit you could just drain into it but then you probably wouldn't be asking this question.
No matter how you go, you need a failsafe way to make sure that if the pump fails the water will not back up into the water heater. The condensate line should have an open end that drains into an open container. The pump should pump from there. The container should dump on the floor before the water level reaches the end of the condensate line.
Depending on the environment, the condensate may evaporate before it collects enough to be pumped so the whole mechanism may behave more like a basement humidifier, which is almost certainly something you don't want.
Copy an existing design
Here's another answer with an approach to doing this the way you want. I'm not advocating this, but I think it solves some of the problems.
The design is stolen from a macerating toilet. In the photo you could analogize the small vessel collecting condensate via an air gap to the toilet bowl, and the trap to the toilet's serpentine trap. The rest is identical, except maybe your chamber and pump are smaller.
I'll just say again: this seems more complex than is warranted. I'm just thinking through solving the problems if you insist on doing it. Isn't there an outside wall somewhere?