Can a septic line make right angles?
I've had a 90 degree L in my main 4" septic line for more than 30 years, and I've never had a problem with it.
Also, I try to keep everything OUT of my septic tank that I possibly can other than toilet tissue and the waste/water that is supposed to go in it, including all else, from grease, chemicals, paint, excess amounts of bleach, all solids and non-biodegradeables, etc.
And I have the tank pumped every five years without fail. (I have it pumped in all years ending in 0 or 5, just to keep it idiot-proof for me. LOL)
I have never used any of those useless "additives" because normal usage provides all of the bacteria necessary for it to operate properly, according to many years aof study by NCSU.
The only thing that I use on my septic system is for root control since our drainfield has a lot of shrubbery and trees planted on or near it. I flush a cup or two of copper sulphate crystals down about three times a year to keep roots knocked out of the drainfield lines. Works like a charm.