[Lswonder]

I want to build a second bathroom beside the first. Can I hook a second toilet drain to the first? Do I have to vent the new toilet, sink or bathtub plumbing? Lswonder

[speedball1]

I want to build a second bathroom beside the first. Can I hook a second toilet drain to the first? Do I have to vent the new toilet, sink or bathtub plumbing? Lswonder

Yes, you may cut in a wye or combination wye and eighth bend in the toilet branch for your new bathroom group. Every fixture that has a trap must be vented.
Most bathroom groups are roughed in like this.
Toilet connects to sewer main or the stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures flood rim.
More questions? I'm as close as a click. Tom