Just bought a home built in 1960 that once used a septic system but is now on city sewer. The old, concrete septic tank in the back needs to be filled as part of the cap has collapsed. The cap is constructed of 5-6 concrete rectangles placed on top of the tank’s walls. My plan is to slide the cap pieces into the tank then back fill with dirt. Do I need to create holes at the bottom of the tank for future rain water to drain? When I bought the house (early February) the tank had visible standing rain water. Forty-five days later that rain water is almost completely gone. The hole at the top of the tank has been covered with a piece of plywood. Evaporation or is water already draining out?