What is the pit ejecting currently? If its sewer then you will definately need to make sure it has an air tight seal.
All connections need to be air tight to prevent sewer gases from escaping. Is there a point on the lid that you can drill a hole and make it air tight? Then also the lid is your access to the pump.. can you make it still be accessible once you add a drain into the top of it? Usually we use a union or similar fitting that can be taken apart to allow the lid to be removed and put back in the same manner..
As fare as venting, yes the sink needs its own trap and its own vent. It could tie into the vent that is there now, first choice is a vent that goes through the roof that isn't the sump vent.. but if they're all tied together then any vent so long as its 6" above the flood level of the sink
I can't see how far down the stack goes.. but just to be clear, it is too high for the sink to reach?
It's just ejecting the floor drain currently which has the furnace and water softener draining into it. Other than that it would be the sink which will be used mostly for homebrewing, cleaning up, etc.
There is definitely enough room to drill into the top and I could use a grommet like mentioned in another comment to maintain the air tight seal.
The vent looks like it goes up to the bathroom above it, probably ties into a bunch of other vents and then goes through the roof. Not 100% sure though...
Excuse my ignorance and my horrible drawing... But is something like this what you mean by tying in 6" above flood level of the sink? Would this work? This is all new to me and I'm just trying to understand and gain some knowledge. Thanks!