Trying to help senior neighbor with washer drain, please help!

[shaven]

Trying to help out my senior neighbor with her washer drain. She said during 'drain' water was spilling back out over the top of standpipe..
I discovered that the drain pipe to the drain was only 1.5 inches diameter and my understanding is it should be 2" ? I dry fit this this morning but am concerned about 2 things (perhaps more, u tell me!)
1) This drain junction is cast iron and the entry of the washer drain is still only 1.5". Trying to avoid costing this lady a major repair can I run the 2" pipe right to within 2" of vertical drain and use a reducing union to drop to 1.5" before exit? The new sandpipe is 30" tall currently.

2) Is the run from my 2" trap at 17" too long and in need of a vent before vertical drain?

I thank you all on her behalf ps trying to add photo

 

[shaven]

Looks like an AAV might help... I don't know what I don't know!

 

[Sponsor]

 

[Jeff H Young]

aav and the 17 inch length are not a problem . most likely not vented properly just guessing but the vent isnt the reason for the overflowing. probebly a stoppage unless its backed up ever since it was built. draw it up and or post a pic

 

[Reach4]

You could extend the standpipe to as much as 42 inches. https://up.codes/viewer/mississippi/irc-2018/chapter/27/plumbing-fixtures#27 That by itself should help.

Are you sure that the cast iron is not two inch?

An AAV does not improve drainage. It keeps a trap from siphoning.

If what is coming out is suds, a SPEED QUEEN 36878 ADAPTER,STANDPIPE may help if you keep a 1-1/2 standpipe. But increasing the diameter of what you can plus raising the standpipe may do better. Do use low sudsing (HE) detergent, and consider using less.