DWV fittings from home to septic tank

[LeakyHome]

Down through the years I've set up 4 different single wide mfg homes (for me to live in). When it came to connecting the home to the septic tank it always seemed a little goofy to me. The pipe into the tank has to have a little drop to it and the available fittings were either 45 or 90 degrees which equals no drop or too steep a drop. Doesn't anyone make some special fittings for this that meet code ? Thanks ....... Alan