Drain re-config

[MisterRogers]

My bathroom remodel requires a relocation of my drains. Basically just a swap of the toilet and shower drains. It's a split level house, and this room is located above a crawlspace, where all of the (ABS) drainage mains are easily accessible. This is about as easy as a relocate like this can be, but I could use a little clarification on a couple of details before I proceed.
The first two photos show the location of the stacks in the gutted room. The old vanity sink drained into the vent stack, and had no further venting. In order to plumb this drain CORRECTLY, should I be adding a wye to the soil stack for the sink drain, and using the existing vent stack takeoff to vent the drain? (there is an upstairs toilet that exits down this soil stack)
http://uberhoser.servebeer.com/tattoocountry/tlf1.jpg
http://uberhoser.servebeer.com/tattoocountry/tlf2.jpg

Also note that the old toilet location is visible and the toilet is now positioned over the old shower drain, approximately where it will be installed.

The plumbing stacks below that floor are pretty easy to get at, and should be pretty easy to change for the new layout. Basically, I need to replace the toilet/shower drain wye with a RH one instead of the LH one that is there (right?) Can someone shed some light on what the heck that large red valve is on the vent stack, and is there anything I need to know about it? There is not a lot of "fresh" ABS to tie into after the old wye is cut out, any pointers on how/where to cut to make the reconnection correctly afterwords?

http://uberhoser.servebeer.com/tattoocountry/tlf3.jpg

The P-trap in the foreground is the current shower drain & approx location of new toilet. The 1 1/2" T off of that picks up a wet bar drain about 15 feet away. The new shower drain will go the same direction as the toilet one in these pics, but will penetrate the floor farther to the right.

http://uberhoser.servebeer.com/tattoocountry/tlf5.jpg

There was a lot of DIY work done (poorly) in this bathroom, and although the plumbing looks like it was properly connected physically, I'm certain that the layout and venting isn't what it was supposed to be. I want to get it right on the redo, and I want to get rid of all the wrong.

I do know my limits, and I know when to grab the yellow pages. I'm confident that this job is within my abilities, but I lack the experience to plan the correct connections on my own. Gratitude for any and all who are able to assist with this.

[FloridaOrange]

What code are you under (i.e. where do you live)?
The fitting will need to be replaced and you may need to rebuild some of your stack to do that.
The bar sink line should be vented independently due to the length of the run.
And yes you would need to wye off for the first floor vanity and run the vent up separately to 42" above the second floor. The reasoning I see behind this is that it appears you have a waste stack vent with the exception of a water closet draining to it.

[MisterRogers]

Canadian plumbing code (Saskatchewan)

Sorry, meant to include that info in the first post...

[wallskev]

I have seen this type of valve use before.

I have seen it used to close the drain line, fill the drains with water and static test the connections before closing in the walls etc ina new construction but normally it is removed before connection to the the final line to the Septic Tank.

[hj]

There are a couple of incorrect things that show up in your picture. Fortunately, because you will have to take out almost the entire system to do your relocation, they will also be removed, and hopefully you will not redo the new one the same way as it is now. I will not say there is ABSOLUTELY no reason for that valve to be there because we cannot see the entire plumbing system, but the possible uses for it are so rare that you might never have to close it.

[MisterRogers]

Good info guys, thanks for the input. Code aside (I will confirm that my final fit up complies with local code prior to installation) opinions on the PROPER way to rebuild this stack?

-remove valve and replace with ABS ??
-replace 3+1 1/2 wye with reverse configuration to accept drains in new locations ??
-add 1 1/2 wye above closet wye to pick up bar drain ??
-add 1 1/2 wye above floor level for vanity drain ??

-tie into vent stack above floor for sink and shower drain vent ??

Should I be moving all of these connections to the soil stack side, or leaving them on the vent side? Pros/cons of that? What issues exist in the current installation need to be corrected?

A previous response made reference to a septic tank. It may not be relevant, but this home exits into a municipal waste system, not a private septic system.

[MisterRogers]

Is it possible that the big red valve was originally installed as a backflow prevention countermeasure as a defense against a city drain collapse? If so, it would have been rendered useless at the point that wye was installed below it, but maybe that is why it was there in the first place?