I got a concrete septic tank ( a second )with out a lid .
Dug a big hole , 2 X as wide as the tank , used steel plate and cable to ancore it .
You need to ancore it down .
A concrete tank will float , I found this out the hard way .
Buryed it with 6-8" above grade
I then built a roof that will slide to the rear , powered by shock cord .
Did this 6-7 years back .
I checked it a few days back .
Still in great shape .
Just need to chop a little grass for the roof to slide .

Johnch