The top of the septic tank needs to be dug up. Than you start making the 2x6 wood frames that go around each cover alowing 2 inches of space around the cover, I used preasure treated wood and deck screws. There are 2 frames of 2x6 wood stacked ontop of each other (4 frames in all).
Now you need to cut a 2 inch thick piece of styrfoam SM or something similar of the same density. It's there to insulate the top, put the foam inside the frame to get an imprint of the cover handle so you can carve it out of the foam. Repeat for the second cover and frame.
Now that the frames are in place, put the patio slabes on top of the frames and foam. I used patio slabs that are 24" x 24" .
Now add pieces of treated 2x4 wood around the slabs, screw to the 2x6 frames, repeat for the other one and you are nearly done...
Now the only thing left to do is to burry the top of the septic tank and around the new frame covers. Let the grass grow back and it will look great. Now this cover ideal is great the next time you need to get you tank emptyed, or as the poopologist said if you have trouble in the winter months you just need to get the snow off to gain access to your tank, makes more sense.