'60s home shower drain reconfiguration

[Robert_Bobert]

Thanks in advance for reading all this:

I'm rebuilding a small 3'x3' shower in an upstairs bathroom in a 1960's home. Existing DWV is copper with either cast copper or CI fittings, not sure on that. In order to remove the old shower drain I had to cut it out completely. There is one 2" vent on the line, between the toilet and the shower. The 3" drain goes to vertical and about a foot lower connects to a separate 3" DWV stack for the other bathroom.

There is 9" of vertical space for this (2x10 joists). Because of the tight space and the size of PVC vs the old fittings, I don't think I can reliably just recreate the existing layout. I also don't know if it was properly vented or vented at all, so I'd like to improve that if I can.

I've attached photos of the existing configuration and a pvc mockup that kinda mirrors it.

Also attached a pic of possible new trap configurations using either a Y or a sanitary T, but I'm unsure if that will present any issues with venting or siphoning.

Here's a link to all photos in an Imgur album

Any advice or discussion is much appreciated, thanks for taking a look.

 

[Robert_Bobert]

was this a bad place to post this question? It seems to be in a similar vein as other posts...