@Teryl_Pacieco Still couldn't find the cleanout, even after the grass was cut. It was raining enthusiastically, so I got soaked trying to dig around for it. It flushed a couple of times last night before backing up again, so now I know the problem is further down the line. Today's solution was to pour a septic treatment down the toilet and hope. If it's not raining after work, I'll try looking for the cleanout again. Thanks for asking!

@KnotKnormal Ohno! Well, hope it works!

@stillinhere It was. It fortunately seems to have resolved itself with the application of two different treatments. I never did find the cleanout.