How to fit waste water pipe into back inlet gully?
I'm assuming this is for storm/rain water runoff and now sewage waste. For a location that freezes in the winter I've seen the recommendation to run the above ground gutters to an air gap and then to the top of a catch basin (hopper) like yours. This allows the melting ice to run off if the ground below is still frozen. If drain is already below ground, or you don't experience significant freezing in your climate, then using the below ground ports should be fine. These side ports tend to be designed to easily knock out, either with a gentle push, or at most with a hammer and screwdriver.