Greetings!

We have a 70's home & the Washer/dryer are in the garage. Currently the washer drains into a 2 1/2" od cast iron pipe that looks to Y into the drain/ vent that exits thru the roof. (All semi buried in the block wall at the moment) No sign of a P trap. I assume there should be one?

On the other side of the wall, there's a toilet! Yes just tucked under the eaves of the house, hidden behind a wall covered in laminated fiberboard, & a really really nice screen door! All added by a former owner, served the pool area. Remodeling that "bath", & adding a sink. I know the easiest thing would ne to tap into the washer drain, but it seems like the venting is all wrong?Do I have to chip open 2 ft of the block wall to add drains & properly vent the washer?
As is:
|Roof
|
||washer
||
|/
|
|Pipe under slab...

Easier solution?

Thanks!
Lee