Washing Machine Discharge Comes Up Basement Floor Drain
My first question here and you pros are a kind, patient bunch. I have spent hours reading explanations to similar problems and I think my issue is my pipes being too small but I was hoping for a little advice.
I have a 1929 house and a Maytag washer in the basement. When it empties (via a tall standpipe through a p-trap then into the drain line) I can see water slowly work up the nearby floor drain (about one foot away) and eventually come up just a bit making a small puddle that very quickly goes back down as soon as the washer has emptied. There is a utility sink connected to the same drain/vent. After reading about similar problems I pulled the washer discharge hose out of the standpipe and let the washer empty into the sink thinking it would slow down the flow (I was amazed at how forceful the washer emptied). That indeed stopped the overflow but water still comes right up to the top of the floor drain.
I turned on both H and C on the sink at full blast and I couldn't duplicate the floor backup. I filled the sink and emptied and no floor drain backup. Nothing else in the house backs up, and nothing else appears to use this drain line. The washer/sink drains are properly vented. The standpipe never overflows. The whole system is 1-1/2" but the old metal pipe coming out of the floor the drains connect to looks wider (like 2-3").
I disassembled the sink/washer drains and snaked the drain and floor drain 25' and both were clean with no resistance at all. I took a hose and ran both H and C on full blast down the floor drain and standpipe and no backup. I can't find any way to duplicate this slight overflow. And I'm reading here about how powerful new machines are and I have old 1-1/2" plumbing.
Is there any way to slow down the discharge rate of the Maytag? Maybe reduce the discharge hose diameter to a smaller size and/or add a few turns? Increase the standpipe length? My floor drain is just a hole with no grate or cover and I can look right down it. Is there a device I can place inside or on top of the floor drain that will prevent minor backflow yet allow the drain to function properly? Like a flap or a ball or one-way valve or something I can retrofit?
Thank you for your time and any advice you could provide would be greatly appreciated.