I just set two 500 gal concrete tanks at the housae. I believe I went 5'4" or so. The hole you dig or better yet the depth of hole you dig depends on many variables. One if yourinstalling tanks for a house you may have to go lower then natural grade. It would be different for a mobile home, you could set it a little higher.. It would probally depend on your ground also. here the ground is flat. But anyway to answer your post it should be more then enough. Also remember to get the bottom flat even if you have to level it by hand, you do not want your tanks rocking. Also when you get them set fill them at least half full of water. They will float if you dont and you dont have water in them.. Hope this helps.. If you got questions email me, I have been installing septics in tx. since I was old enough to carry pipe..