Hello,
Dug 40" hole for 30" Everbilt fiberglass sewage ejector pit, backfilled pit withsome pea gravel, and of couse it rained several inches that day, so I have a floater now. What is the best method or means that you all have used to fasten the pit flush to floor hole, thereby preventing buoyancy and future pipe movement??

Note, not all the screw holes in the pit lid will line up with solid concrete, and I do want to be able to open the lid without destroying anything... help please.

The fact that the holes don't have a mounting is a problem. Sounds like this is an afterthought. Most are set in place and then the floor is poured. At this point I would either pour concrete around the pit box and then screw it to the floor or make a PT wood ring bigger than the pit box edge, anchor that to the floor and screw the pit box to the ring.

JM,
On new & remodel installs, once we have the ejector tank level and set at the correct elevation we'll fill the tank with water and then cement it in place... no other means of fastening is needed