EDIT: PHOTOS ARE IN POST BELOW:
I am installing a new (2nd) washer in my basement. From where the washer sits I am trying to decide on the best way to drain it. It happens to sit directly below an upstairs washer (maybe a foot to the left of it). All water and waste lines and the main soil stack are copper. There are a few ABS connections where I assume someone added vent lines at some point.
The standpipe for upstairs washer enters the basement into a cast iron trap and extends over 2 feet and then drops again into a horizontal drain line leading to the main soil stack. There is a bathroom sink that drains into the basement about 3 feet away from the wall that bends toward the standpipe trap before making a 90° turn and entering the same horizontal line as the upstairs washer. This is 1.5 inch copper and there is a section right below the trap for upstairs that could cut into and connect a drain for the washer. The problem is that I only have 15 inches from the ceiling to where this connection would enter the hroizontal line. If I leave room for the bend in the washer drain line, that would only leave a realistic 12" standpipe and I am unsure if I could make that work since it would connect into a 1.5 drain pipe. Even if I used 4" standpipe it would have to reduce in such as short run I am not sure it would work.
Also of note in this option is that there is a 2" vent pipe in the horizontal drain run about 5 feet to the right of where the washer sits, so if I could get the water to drain here I am thinking the venting would be ok to handle the new washer p-trap. Unfortunately, this vent is located right at the top of the basement block so it has two 22.5° connectors with no straight pipe before it dissapears behind the studs and wall. There really is not any way for me to cut into it to merge another vent and still have any place to connect new piping to - I will not have access to be able to glue the new connections.
At some point someone cut into the main 3" copper soil stack about 18" above the basement floor, soldered in a 1 foot run of 1.5 inch copper pipe pipe followed by a 1.5" shut-off valve followed by a 1.5" ABS p-trap and then a 3 foot 2" PVC standpipe for a water softener to drain into. I am guessing the shutoff valve was used so that it could be closed in the event of a sewer line back up. I have no idea why they used an ABS trap with a union piece to a PVC standpipe, but that is what is there.
From where the washer sits this location is 7 feet to the right, it hits a 90° corner of the basement and then is another 13 feet to the trap.
If I wanted to use this lower entry into the soil stack, could I just drain the washer using a standpipe without a p-trap, have the line just bend into a horizontal run that connects into a wye in water softener standpipe and use that trap? I am thinking in effect this would almost be the same as directly draining into the softerner standpipe, only it is actually 20 feet away. The 2 would never be in use at the same time. If I used the hose that is already connected to the washer, used 2" PVC with an 18" standpipe and 1/4" per foot slope, this would put the entry into the standpipe about 12" above the trap by the soil stack. Would that be ok?
My concern is that if I remove the p-trap from next to the soil stack and put it below a basement washer standpipe I would need to vent it and there is no logical connection point (remember, the closest vent out side of the soil stack itself does not appear to be one I can realistically tie into). I guess an air admittance valve could be added, but then what would I do with the water softener drain since that would need to be much closer to the stack?
Hopefully someone can guide me on the best options here - let me know if I am being unclear - thank you!