No other backups that I have noticed. the washer is in the basement so there are no lower pipes that I can see.
So no floor drain that feeds the sewer.
Its a sewer system. The only backups are from washing clothes. We've only lived here for about 2 years but within that time I have not seen any pipes being replaced.
If the backup is only suds, that could have one kind of solution. The Amana 40008101 or Whirlpool 40008101 is intended to suppress suds backup from a 1-1/2 laundry standpipe. If that is the solution, then the Liquid Plumber probably would not have helped as long as it did.
What would probably be best is to do a mechanical cleaning of the drain. If there is no cleanout currently, you could maybe install one if the pipes at the standpipe area are visible. Perhaps post a photo that includes the pipes on the output of the standpipe trap.
You might even be able to clean through the standpipe. While not the best, I used
RIDGID PowerSpin Plus Model# 57043 through a trap. I was expecting to disassemble the trap, but I tried through the trap just in case it worked. Yes, the head is much smaller than you would like. Something bigger would be better.