I am not sure about this issue with the drain , I think what you are going with is the right choice . As for the w/d placement it would give you more folding space if tyou did a counter to spacn both machines after you seperate them Th e only thing that makes me hesitate is even with my machines close together I drop stuff on the way from washer to dryer . I think it could look pretty cool seperated though.

I would connect both to a 3 inch drain, however you do it! Otherwise ? Separate entirely add a drain for sink.

I would not want a sink between the two appliances, UNLESS you always load washer to large basket..... to dryer. You'll drop on the floor if you don't.

Where is the plan for the space?

DON'T put the sink between the W&D. But DO get a good, deep utility room sink and plumb it next to your W&D in your laundry room. They come in all materials and price ranges, but you should get one of approximately this size.

https://www.homedepot.com/p/Ruvati-21-in-x-18-in-x-12-in-16-Gauge-Stainless-Steel-Undermount-Deep-Laundry-Utility-Sink-RVU6121/311470121 

If you can have a countertop where you can undermount the sink -- that would be ideal. I can't really picture what the layout of your laundry room is; if you can give us a diagram with measurements perhaps we can offer specific suggestions.

As far as the drainage -- don't have the washer drain into the sink. Either put a drain pipe behind the washer that can drain into the sewer line, or do as your plumber suggested and run a separate pipe in your basement, which I guess would work although I can't picture exactly what your plumber is suggesting. But your plumber knows the code and your specific situation so I would trust him/her.

Be sure when you arrange your appliances that the doors to the W & D open correctly -- that is, if you have a front-load washer and dryer, and the washer is placed to the left of the dryer, then the washer door should be hinged on the left and the dryer door should be hinged in the right. That way, you can open both doors and put the washed clothes directly into the dryer without having the dryer door in the way.

Hard "no" to draining into the sink if you are re-doing the room. Different if you had no other option - but you do. Code calls for a 2" drain to the stack - not a 3" as was suggested by someone else. A 3" drain is completely unnecessary.

Sink in middle of washer/dryer would make me angry every time I used the machines.

A floor plan of the room and an elevation of that wall would be super helpful.

Depending on the height of the window, you can use front loaders on a custom built platform so you get them off the floor, but don't block the window (as much). Another plan would be stacking a front loading set on one side of the window - but that puts the washer on the floor. Not a great place as far as bending over to move clothes from washer to dryer but still better than a sink in the middle.

Thanks everyone! Here are some pix of the layout. Don't judge my mess, we were demoing the closet... I'm not going to get a typical "utility" sink, but probably a deep stainless one with an optional "cutting board" top that I could place on top for added folding space. You'll see in the interior pic that my washer n dryer are currently centered below the window but if i were to keep the sink to the left and not under the window, my machines would be pushed to the right. This is a gas dryer so we need to keep them on this wall (really don't want to drill more holes into our brick exterior). The only other option is a stackable to the far right n we'd have to move our light switch. the part by the garage door is going to be a few very tall built in cabinets for brooms/cleaning supplies etc. and a drop zone. The space has 3 doors and we go in and out a lot. I'd initially wanted a dog shower in here, but I've given up on that dream.

I think your suggestion to move the W&D to the far right and have the utility sink with its cutting board to the left of the washer is the best option. Stackable W&D units are not ideal, in my opinion -- hard to service, some of them have the dryer controls and clothes drum too high to reach, etc. Better to keep them side by side since you do have space. I might consider putting a pocket door between the laundry room and the family room; I always prefer pocket doors unless there is a compelling reason to have a swing door (like for an exterior door). Or maybe you already just have a doorway there and no door at all? The tall built-in cabinets are a great use of the space by the garage door. Good luck and keep us posted so we can see the final result.

Thanks, yes we planned on at least a modern "barn" door b/c we have a vent there we can't do a true pocket. That will help conceal any built up laundry/mess, however we do want this to be designed well as we've redone our entire home so far and this is one of the last rooms. I want it to be as functional as possible but also look nice.