It doesn't have to be a clog, whoever plumbed my house did so with bad angles, so the rush of water from my washing machine tends to back up and come out a nearby floor drain.
I wasn't about to tear up the concrete floor to find the problem.
Laundry was upstairs and basement is unfinished so we rerouted the washer disharge line to another line. Works fine now.
You never get the fruit if you don't go out on the limb!