Venting for 1st floor toilet on slab foundation

[AllIn1]

I am remodeling my house, and since all the walls are open I decided to repipe my plumbing. I noticed that a few of the ABS vent lines are leaking when it rains, so I was thinking about redoing the sections that are leaking. My question is regarding the first floor bathroom, and how the toilet vents out. In the picture, the thick 3in pipe is the drain line for the toilet and shower in the bathroom on the second floor directly above this bathroom, as well as the drain line for the toilet on the first floor. The w/o pipe coming out of the slab right next to it are what appear to be the vent lines. One of the pipes is 2in the other is 1 1/2in, and they both tie into the same vent and go out the roof without anything addition tying into it. Is it normal for two vents to come out the ground and tie into each other like that? What is the purpose of this? Also the shower upstairs vents through the sink vent that is on the far left, but I was thinking about changing that so it ties into the same vent as the toilets, would that be acceptable?

 

[Jeff H Young]

pipes leading to second from first that are shown in image 2436 only the the 3 inch can be used for drains above . yes totaly normal to tie the 2 and 1 1/2 lines and vent out roof.
your last question isnt clear but in general yes there are times when a toilet and shower can share drain and vent

 

[Sponsor]

 

[AllIn1]

pipes leading to second from first that are shown in image 2436 only the the 3 inch can be used for drains above . yes totaly normal to tie the 2 and 1 1/2 lines and vent out roof.
your last question isnt clear but in general yes there are times when a toilet and shower can share drain and vent,

Hi Jeff, thanks for the reply, so if the second story shower shares both the drain and vent with the second story toilet, can I change the vent to that the second story shower so that it shares a vent with the first floor toilet, but shares the drain with the second story toilet, essentially using a different vent stack than the drain?

 

[Jeff H Young]

as long as the vent from the first floor joins the second floor shower a minimum of 6 inches above the shower dam n you are good