Bath draining help

[CJLockhart]

Hi all,
This is my first post, so I apologize in advance if I've put this in the wrong section or messed up any technical terms.
I'm redoing my dining room and had the ceiling torn down, and so decided to do the plumbing for an upstairs bathroom above said dining room. The bathtub has a drum trap I was going to replace with a P-trap (not a big issue) but there's a vent pipe connecting just after the drum trap that I'm wondering on the status of. Can it be removed, or should I just tie it in after the P-trap with a wye? The 3" vented stack for this line is about 6' away (next picture) if that makes any difference.

Drum Trap Link
Following along the same drain the tub (and lav sinks) empty into this 3" elbow with a 1.5" drop on the side directly under the commode, and I'm suspecting that's not allowed. I think these are used more for venting, and not much for flushing sewage accidentally into your tub drain. Should I rebuild this section to include a 3x3x1.5" wye (or sanitary tee) after the elbow from the commode?

Commode Link

Thanks in advance for any advice you can share.
-C

 

[Reach4]

Drum traps don't usually have vents.

The lav drainage is probably wet-venting the toilet, and I guess the drum trap.

However these fittings are not what you would put in today. If you make the changes, you will need to use wyes to join waste, such as the lav to the shower drain and the toilet to the combined shower+lav.

Ready to insert two wyes?

 

[Sponsor]

 

[John Gayewski]

Pictures or diagrams are better than trying to explain this.

 

[CJLockhart]

Pictures or diagrams are better than trying to explain this.

Thanks John, good call. I linked URLs in my post to reduce clutter, but might have made it cumbersome.
The red arrow and line are pointing to the vent that goes straight up through the roof, it's only connected to the drum trap (with a 1.5" Tee)

If you follow the bath drain to the left of the picture, you get to one of three stacks our house has.

The lav sink comes in from the left (blue), the bath comes in from the right (green), and the commode comes down from the center. My primary concern is that 3" elbow just under the toilet which has a 2" outlet to the side (where the bath & lav connect). The 3" stack goes vents up through the roof as well.
So, I find myself wondering what is the use of the vent by the bathtub (should it be removed). Because I desperately want a roofing project as well.

Thanks for your help!
-C

 

[CJLockhart]

Can anyone provide some help/ideas on the elbow below the commode (second picture)?

Thanks,
-C

 

[John Gayewski]

The vent for the bath is just that a vent for the drum trap. Your plumbing doesn't look that bad can I ask why your changing it?