Hi everybody,

First time posting, this forum has been a huge help to me as I work on remodeling an old house (1940s). I'm decent with most trades but haven't had a lot of plumbing experience and need some advice before attempting to add a bathroom on a concrete slab. I will probably be hiring a licensed plumber to do the fittings and make the connection to the sewer line (the long black horizontal line), but I'm very price conscious at the moment and want to do as much as I can to knock the price down (i.e. get the trenches cut and dug etc...) so I won't take up much of his time.

I'm in Houston, Texas and we follow the UPC 2006, but also allow AAVs.

Attached is a layout of the proposed bathroom. This was an addition to the house and was poured on slab (the brown wood floor area). The light brown area is the old porch that was taken out and is now just interior dirt. I've trenched through the dirt and was hoping to make as many connections in the light brown area so I could minimize cutting the concrete as much as possible. The red lines are the drain lines, with the main line from the toilet being 4" and the rest being 2", except for the 1st sink, which was 1 1/2" (2x4 exterior wall). I was also going to run 2" vents everywhere, connect them in the attic and run 1 roof penetration (not sure about the size).

The double sinks on the exterior wall concern me because of the studs that the drain pipe will have to pass through to get to the 2nd sink. Was considering using AAVs here to minimize further cuts to the top plate and working in a low attic. Also considered tying the sinks in directly since they're close to the old sewer line (black horizontal line) but the old sewer pipe is concrete and I'm concerned about connecting to it at the sink and again at the main drain because I don't want to create a section of concrete pipe between 2 flexible connections that could create a belly.

My other concern is that I want to minimize roof penetrations. There's already a 2" vent in the attic from an old drain that I was curious about tapping into. I would like to tie all my vents together in the attic and use that vent or enlarge it somewhat.

The last thing is that the washing machine drains goes through the standpipe and P trap and drains into the same vent as the tub. I'm not sure if this is a permissible wet vent, but I was thinking I could connect them with some sort of sanitary cross like a double vanity uses.

Just wanted to get thoughts on whether this would generally work for a drain and vent layout. I'm aware that the shower needs to be vented within 5' and the first sink must be less than 42" from the other for venting. If anyone has any other ideas of things I can do to help knock the cost down a little. Please pardon my lack of knowledge - I really appreciate the help. Feel free to ask any questions and I'll respond ASAP.