James, You say you have the water hooked up. Are you absolutely sure you are using no water? A single toilet leaking 1 quart a minute would fill a standard 1000 gal septic tank in three days. It could be possible for water to back up from your leech field, but that would mean your water table would have to be so high that it is filling the distribution pipes and backing up to the tank. Hard to believe that you could have gotten a septic permit with those type of water levels in the soil. One thing, it is a good idea to let the tank fill after covering it up. If heavy rains come after you bury it, and it is empty, it is possible for it to float upwards and wreck the connections.