I like to keep the water level in the pump return section as low as possible. Well the trick is to keep enough water for the pump to start back up again after a power outage. Yet not overflow the sump. #1 for me is not overflow the sump so that's why the water level is so low in my pump section of my sump.
I'm not 100% sure what your question is, sorry. I have two bulkhead holes. One is for a drain that goes to my trees outside and one is for the pump.
The "trickle" system is the key to the whole set up and very easy to use. I put in 1 gallon of water into my fish tank and the extra water flows down to my sump and goes out the drain. Every hour 1 gallon, every day 24 gallons and so on. No more water changes and my trees out side love the water!