I'm remodeling the washer room and have a question bout my drain and vent pipe. I'm buying new units and I want to extend the drain pipe to the back of the washer. Currently it's on the side close to the front of the washer.  The picture shows on the left what it use to be.  Once in a while it would back up and spill out. So with the new units coming and wanting to go 2", I was thinking of breaking the cast iron vent, put in a rubber tee and capping the old 1.5 drain pipe. I'm not going to try and fit it in the wall so it'll exposed. Vent pipe will then go 1.5 up out the roof.
What do you guys think?
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  [1]: https://i.sstatic.net/LoVv4.jpg