Replacing the Drum-Trap with a P-Trap

Whenever I start a home project, I look around the interwebs to see if anybody has done it first.  I love it when I find tutorials and see that DIYers have done it themselves in the past.  In that spirit, I’m going to blog about my latest plumbing adventure.  Hopefully somebody will find this in the future and be encouraged by my work.*  

A few weeks ago we noticed that our bathtub was draining very slowly.  So slowly  that it would take about an hour for our shower water to drain completely from the tub.  This was gross because while we showered we stood ankle deep in our dirty bathwater.  Eww.  

We had a plumber friend come over and snake the drain, but he could only get the snake five feet into the drain.  That didn’t solve the problem.  ”I think you have drum-trap,” he said.  ”It makes it really hard to clean your drain because you can’t get the snake past the drum.”  

"What’s a drum trap?" I asked.  

He explained that modern drains have what’s called a P-trap.  The water flows into this trap before going into the main sewer line out of the house.  The purpose of the trap is to prevent gases from the sewer line coming up into the house, like you can see in this wikipedia article.  He told me that houses built before the 70’s don’t have P-traps, they usually have drum-traps.  Drum-traps are evil incarnations designed by stupid people.  A drum-trap looks just what it sounds like.  The drain water goes into the bottom of a cylindrical drum and exits out the top.  

It looks like this: 


My plumber friend then told me that I should probably get somebody to replace the drum-trap with a P-trap because we’ll never have an easy time cleaning our drain if the drum-trap remains.  Get somebody to do it?  You mean pay somebody?  Do you know me at all?  For better or worse I’m doing this myself!  Challenge accepted!

The first thing I did was take down the ceiling in the basement bathroom to get a look at the trap.  Here it is in it’s glory with some arrows to help you understand the flow.


Gross, right?  It looks like there’s a way to open the drum from the bottom so I tried that first.  No go.  It was sealed shut with 50+ years of dirty bathwater.  The whole thing had to come out.  

I borrowed my dad’s reciprocating saw, bought a metal-cutting blade, and inspected the pipes for the best places to cut.  I decided to cut here and here: 


The blade started cutting easily enough, but as soon as I busted through the pipe I was greeted with a shower of black sewage.  Literally, a shower.  The blade of the saw, alternating at what felt like 1 trillion revolutions per second, sent the black water (if you can call it “water”) in all directions, including onto my face and down my arm into my armpit.  It was everywhere.  I stopped for a minute.  Gathered my thoughts, and decided to just go at it.  It had to be done.  I donned some safety goggles and went to town with renewed vigor.  After a few minutes of the worst shower of my life, the pipes were finally cut.  The drum-trap was out!

Next, I had to remove the old metal piping from the T-joint so I could start clean with more modern ABS piping.  I bought a 18” plumbers wrench at Harbor Freight for $7.99 and borrowed a long pipe from my neighbor’s shed to get additional leverage.  After liberal application of WD-40 the old pipe came out like a charm.  I was most worried about this step.  I thought the old pipes would be sealed shut but I was pleasantly surprised.  To feel the pipe working lose almost brought a tear to my eye.  

Here is the metal piping and the trap completely removed and disassembled.  So gross.  


After the old metal pipe was out I snaked the drain all the way to the main sewer line.  It was clean was a whistle; the clog was definitely in the piping near the trap.  I next inserted the male ABS adapter into the existing T-joint.   I applied a coating of teflon tape and used the pipe wrench for the last few turns to get the adapter nice and tight.  


On the other end of the line, the line closest to the tub, I used an ABS trap adapter to connect to the tub pipe.  I cut some additional ABS pipe, used a couple of 90 degree joints and fit the puzzle pieces together to complete the contraption.  I inserted the ends into the adapters for a dry run.  Voila!  My P-trap fit like a charm.  I disassembled the contraption and applied a heavy coat of ABS cement to all the joints.  I stuck all the pieces in and wondered whether it really would be this easy.  

This is how it looked when I was done: 


I let the cement cure.  A few hours later I had Andrea run the water from above.  She said it was flowing very quickly down the drain.  I carefully inspected every joint and couldn’t see a single leak.  Mission a-freaking-ccomplished.  

I can’t tell you how happy this made me. I started the day fully expecting to call a professional plumber to help me complete the project.  In the end, everything went very smoothly.  I couldn’t have asked for a better outcome.  The next project is building an access panel where I cut the hole in the ceiling in case I need to access this area again.  

*But mostly I want to brag.