I'm posting here to try to reach someone, anyone who will know the answer to this...I've already spent more than three hours searching the web with no results... I'm plumbing in a new septic tank; this is my first time...I'm ready to lay the drain pipe from the mobile home to the tank...and... There's a soft plastic "cap" set into the tank opening. There's no opening in the cap. When I pushed on it I could feel something solid behind it...I took a hammer and gently tapped the cap in the center and it sounds and feels like there's concrete behind the cap - about 1/4" to 1/2" behind it... So, how do I get the drain pipe into the tank? Do I punch out the concrete behind the cap? Is there supposed to be a baffle behind the concrete behind the cap? Or do I have a defective tank? Please help if you can, or refer me to someone who can. I need to get the septic tank plumbed in so we can get it inspected and move in...it costs too much where we live now.