Maximum Inlet Pipe Angle to Tank

We are renovating and re-plumbing a house that has two existing concrete septic tanks. All of the drain/waste lines are being replaced including the inlet lines to each tank. However, the permit does not allow us to move/alter the tanks or touch the drain fields in any way (luckily both are in good working order).

The existing tanks are set at odd angles relative to the house. Installing the inlet pipes perpendicular to each tank wall is going to be impossible. What is the maximum angle (horizontal plane) that the pipes can come into the tank?

1/8" per foot is recommended, I would not go anymore than 1/2" per foot with 4" pipe

Check your local code. In Florida, we had to drop from the house main drain by means of a 45 degree fitting, then approximatly 2' of pipe and then another 45 fitting before entering the tank.