Revised DWV

I'm still working on a venting solution for this unvented bathroom. Based upon the previous recommendations from hj and FloridaOrange (thanks guys), I have come up with a different layout. I've added cleanouts on the main line behind the toilet and on the vanity line. I want to run a single vent up from the double fixture for the vanities, because that is the easiest wall to work in. So the questions are:

1. With this layout, can I have just a single vent?

2. Can the vent be 1-1/2", or does it need to be 2"?

Again, thanks for the help.

Tub to vent is TOO far. Why do you show the vanities one above the other, and WHERE is their vent? If you have the toilet pipe in the wall with a cleanout, why isn't IT continuing up through the roof? Most inspectors would NOT approve that toilet routing since it goes back, down, and forward before reaching the "vent". The tub drain could NOT cross over the 3" and then drop down into line with the 2".

Sorry hj, I didn't make myself clear. This is an overhead view. The toilet cleanout does not exist yet, I have to add it. The tub drain would come into the side of the 2", not drop down. I can leave the tub as it is currently connected (to the kitchen drain), but it is then 16' from the vent. I thought this might be an improvement.

While I'm a big fan of wet venting I think you are going to have to add at least one more vent. IIRC a 3" can be no more than 10' from the vented line and 6' for a 2" line, based on FL code which is based on IPC.

Your drawing looked like an attempt at an isometric layout more than a plan view. Unless the 2" to the lavatories is "rolled up" above the level of the 3" line, which you do not show being done, the tub's drain will HAVE to drop down to it. But as a practical matter, the line is too long anyway, so you will have to add a vent which makes its elevation immaterial.

Revised

Appreciate the feedback. When this house was built in the late 60's there was not a lot of attention paid to code in rural Nevada, although the county does show that the permit was finalled. In any case, the house has two vents. One is at the back, and serves the kitchen. The other is at the front and serves two upstairs bathrooms and the laundry. This bathroom is in the middle on the lower level, and has no vents or cleanouts. We discovered this when we had a drain line freeze last December and Roto-Rooter couldn't readily access the blockage. We've now installed proper hangers and have all the drain slope problems worked out. Since I was down there working on pipes, I thought I would install cleanouts and try to get some sort of venting into this area.

The tub runs to the line from the kitchen, and connects to that line 16' from the kitchen vent. The toilet is the first fixture on the line that ultimately goes out to the street, and the vanity and the kitchen join that line later. As you guys explained before, big past small isn't good, but that's the way they built it. Obviously, nothing has ever drained properly in this bathroom.

In my revised plan drawing, I have decided to leave the tub as it is, since it does not appear that it is going to be easy to vent it. I want to extend the 3" toilet line to the wall and install a cleanout. I want to extend the 2" vanity line to the wall and install a cleanout. I can run a vent up from the vanities, which should make them work normally and help the toilet to flush. I would prefer not to have to run a vent up from the toilet because that would have to be surface mounted on the exterior.

1. With this revised layout, can I have just a single vent?

2. Can the vent be 1-1/2", or does it need to be 2"?

Again, I don't have any hope of getting it up to code, just to get the fixtures to drain better.

Thanks again for all the help.

Big past small, or small past big is immaterial, IF the piping is done correctly. IF it is not, EITHER one could be a bad installation.