I am building a barnament, a barn with an apartment, for my family to live in while we build a new house. I am doing everything myself, some this I have never done before. I am going to be installing my first ever septic tank. I have a 500 gallon low profile poly tank. My understanding is that I will want the main drain coming into the tank to be no more than a quarter inch per foot of fall. Do I gravel the drain line coming in? If so about how much gravel should I put around it? Then do I gravel around the tank? How much do I put around it? My research has indicated that I believe it needs to be compacted as well? Then I need to fill the tank with water as I fill around it. Do I have all this correct?