I am tying in to an existing septic system. To get the slope required from the house to the tank I will have a tie in point that is about 1 inch lower than the existing tie-in. This puts me closer to the outlet which will have sewer standing in the new line. I am wondering if I can drop the outlet or if I need to, and how long do the downpipes need to extend into the tank? Any and all advice would be appreciated. Thanks

I'm concerned about waste water standing in the line. Seems like it could cut down the flow and lead to solids more likely to clog up the line between tank and house. To correct that you would also need to lower the outlet on the opposite side that goes to the drainfield, or use a larger diameter outlet pipe which would lower where it exits. But since the drainfield is a lot larger than the inlet pipe which is typically 10 ft or so that would be kind of expensive. Also lowering the inlet by one inch cuts down the capacity of your tank which is typically sized to the no. of bedrooms in your house. Could you tweak the location of your lowest, last fixture in the house so you can use the existing line? Could you enter the tank in a different spot to eliminate that extra inch? For a 4" diameter pipe I would extend it 8" or so into the tank then the downward bend so solids go to the bottom of the tank.