How to Install Drain Lines for a Double Bowl Bathroom Sink

Double sinks only use one p-trap.

Double bowl bathroom sinks have separate drain lines that converge before the p-trap, which attaches to the stubout or the pipe that comes out of the bathroom wall below the sinks. How you configure the sink's drain pipes and where you join them together depends on the location of the stubout in relation to the sinks. If you have not installed double bowl sinks before, even if you have experience with single-bowl sink plumbing, follow the installation instructions carefully to prevent future drainage problems with one or both sinks.

Things You'll Need

• Tailpiece pipes
• 90-degree pipes
• Sanitary tee
• P-trap
• Pipe riser
• Double 90-degree tee pipe
• Measuring tape
• Hacksaw
• Straight lengths of pipe
• Pipe wrench

Instructions

1. Thread tailpiece pipes of the same length to the sinks' drains. Thread two 90-degree pipes to the bottom of the tailpieces if the stubout pipe sits between the two sinks. Install a sanitary tee onto the bottom of the tailpiece of the sink that sits nearest the stubout.

2. Attach a p-trap to the stubout. Thread a pipe riser to the top of the p-trap. Thread a double 90-degree tee to the top of the p-trap if the stubout sits between the sinks.

3. Measure and trim horizontal pipes to connect the 90-degree pipes to the rest of the plumbing; use a hacksaw to trim, as necessary. Attach the horizontal pipes to the 90-degree pipes and either the sanitary tee or the double 90-degree tee. Trim the pipes further if the pipes do not attach to each other without bowing.

4. Tighten all of the pipe connections by hand. Run water down both bathroom sinks and observe any leaks. Use a pipe wrench to tighten leaking pipe connections, turning them 1/8 turn at a time until the leak stops.

References

• Fine Home Building: Installing a Kitchen Sink
• This Old House: How to Install a Kitchen Sink