Sump Pit Install

I’m new to the site. It’s been discovered that my 2 floor drains and my shower in my basement are actually connected to a gray water cistern that is somewhere that can’t be located (3 companies tried) Anyway, I figured the easiest way was to connect the cistern piping to drain lines that go to my septic. I broke up the floor and dug out to find a drain line about 1.5 feet under the concrete. I then dig where I expect the cistern lines and find them about 3-3.5ft down. Now I know water doesn’t go up hill well. So I figured I was going to have to install a sump pit where one of the floor drains are at in my utility room and have it pump into my main 4” line that is there. My question is though, since the cistern lines are 3-3.5 ft down and the avg sump pit is only 24 inches deep, how do I make this work? Do I have to dig 5-6ft down and do some sort of manhole to access the sump pit cover so it’s servicable in case of failure?

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