You should never build anything on top of a septic tank. Unless I am misinterpreting the question?
There is an Old Blue Chair for each and every one of us, we just have to find it.
2006 GMC Sierra 2500hd crew cab
BOSS 8'2" Power V
Hustler X-one 60"
Toro Proline 36" wb w/t-bar controls
JS46 22" walk-behind (wouldn't recommend)
Shindaiwa T254, Echo trimmers, chainsaws, pole hedge trimmer, pole saw, hedge trimmer
Shindaiwa 633 and Husqvarna 130BT blower