There’s a drain in the utility room with the washer and dryer. I should’ve tried liquid plumber but hopefully the plumber will get here soon.I had that problem too, when the washing machine drained it would come out of the powder room toilet that was right next to the laundry room. I guess they share a line. I actually poured two bottles of liquid plumber into the drain where the washing machine drain tube goes… waited a day or two and that seemed to do that trick. I was surprised because I havent had much luck with liquid plumber.