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Install P-Trap — Connect Drain to Waste Line

Intermediate24 hours

Part of project

How to Install a New Bathtub and Drain Assembly · Step 7 of 9

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In this video

Install the P-trap. Dry fit the pieces first to get the correct height and alignment. Cut a vertical piece of pipe to connect the horizontal drain assembly down to the P-trap inlet. Ensure there is a minimum of two times the pipe diameter (e.g., 3 inches for 1.5-inch pipe) of straight pipe between the P-trap outlet and the TY fitting to prevent siphoning. Once measured, glue the P-trap into the TY fitting. Connect the union joint and tighten by hand, using channel-lock pliers for a final snug turn if needed.

Goal: Connect the horizontal drain to the vertical stack and prevent sewer gas from entering

  • Per plumbing code, ensure there is a straight pipe section of at least two times the pipe diameter between the P-trap and the vent tee (TY).
  • Hand-tighten the union nuts on the P-trap and trap adapters first. Use pliers only for a slight final tightening to avoid over-tightening and cracking the plastic.

Used in this video

  • Tape Measure (Tool Type: Measuring Tool, Measuring Tool Type: Tape measure)Measuring the length of the vertical pipe section.
  • Channel-Lock Pliers (Tool Type: Pliers, Pliers_Type: Channel-Lock) · optionalProviding a final snug tightening on the P-trap and trap adapter nuts.
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FAQs

The tool list includes some unusual items. What are the truly essential tools I'll need for this bathtub installation, focusing on the specialized tasks?

Beyond basic hand tools like a tape measure and screwdriver, you'll definitely need a reciprocating saw for demolition, a level, pipe wrenches or channel locks for plumbing, a caulk gun, and a drill for securing the tub. Ignore items like bistro sets or candles from the provided list; they are not needed for this project.

This project involves demolition and plumbing. What are the most crucial safety precautions I should take throughout the process?

Always wear appropriate personal protective equipment, including eye protection, work gloves, and a dust mask, especially during demolition. Ensure the water supply is completely shut off before disconnecting any plumbing to prevent flooding. When lifting the new tub, use proper lifting techniques or get assistance to prevent back injuries.

The project is rated 'intermediate' with an estimated 24 hours. What aspects make it challenging for a DIYer, and is the time estimate realistic?

The intermediate difficulty stems from the precision required for plumbing connections, ensuring the tub is perfectly level, and potential subfloor or stud repairs. The 24-hour estimate is for active working time, not calendar days; expect to spread this project over several days or a long weekend to account for drying times and unexpected issues.

What are the most common mistakes DIYers make with the drain and overflow assembly that lead to leaks, and how can I prevent them?

The most common mistake is improper sealing. Ensure you use plumber's putty or silicone caulk correctly around the drain shoe and overflow gasket, making sure all connections are tight but not overtightened. Always perform the leak test step thoroughly before enclosing any plumbing, as undetected leaks can cause significant water damage.

Transcript
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from the trap to my sink drain assembly above it. And what you want to make sure is that you have two times the pipe diameter in between the p-trap and the T that it's discharging into. So you can see I had to turn it over a bit so I could get my three inches. It's inch and a half pipe, so I need three inches of pipe in between. And what that's for is so the sink doesn't siphon itself. It's getting a little dark here and bear with me it's coming back. I was trying to do the union p-trap up while holding a camera so that didn't work so well. So you'll see here I'll glue my p-trap in. Make sure that my elbow is straight there. And then once that's ready I can glue on my vertical section for the p-trap. Now I like union p-traps. I know some people have a problem with them. I've never had a problem with them. I like them. I'll have to put my camera down again here just to lock this nut. So please bear with me. Okay so now I'll get my union p-trap locked into place. I don't like to put tools on these. I just like hand tight. Now if you don't have a great grip you can use a pair of channel locks or adjustable pliers and just get them snugged up if you if you need to. This is the last part here. You can see I've got my cheater vent coming off the top. And I like to put them right up as high as possible. Now I think they say in the instructions that you need a two or three or four inch piece of pipe. I like to go as high as possible.

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