My tanks are 500 gallon septic tanks with a tee inside the tank on the outlet. The tee has a plug on top so you can get in to clean it. The lower leg of the tee, goes down about 2'. That leaves room for the muck to gather in the bottom of the tank, the water to drain out the riser pipe, and any oil to float on top. Make sure your opening on top of the septic tank is cut big enough for you to access the tank for cleaning. I have catch pans built into the floor above the tanks so catch a lot (not all) of the mud before it gets into the pit. If I did it again I would figure out some kind of coupler so that I could remove the tee while cleaning out the tanks.