Tub p-trap

[Java_Bob]

Hey guys, I plan on changing out a old tub. The existing waste line is all copper, and the P-trap is a monster with a top that unscrews, question I have is would you leave that in place or replace with a new P-trap..

[LazyPup]

For me this question is a total no brainier.

What you are describing is actually not a P-trap but rather it is a Drum trap or sometimes called a barrel trap. In theory they were a very good idea, especially when the advent of the skirted built in tubs came into vogue because the barrel trap could be installed on the drain line in front of the tub with the screw cap flush with the finished floor in an accessible location. That provided an immediately accessible cleanout on the drain line, thus negating the need of a 12”x12” service access panel from underneath or through an adjacent wall to access the pipe when it is necessary to snake the drain line. In theory that idea worked fine, but in reality there was a serious problem. One of the major gasses that comprise sewer gas is hydrogen sulfide (SO2) and when hydrogen sulfide combines with water vapor (H20) it produces sulfuric acid (H2SO4). The overall bodies of the barrel traps was heavy enough that they could withstand the minor amount of acid produced for 50 to 100 years however water also clings to the threads of the trap access cover by capillary action, and as that water is converted to acid it etches away at the threads. In some instances the threads are etched away until they can no longer hold the cover in place, but more commonly, the corrosion caused by the acid literally welds the cover to the trap body and it is nearly impossible to remove the cover for access.

In the beginning I stated that the decision to change out that trap was a no-brainer. That is because in the late 50’s or early 60’s they began amending the plumbing codes outlawing the installation of S-traps, barrel traps, drum traps, crown vented traps or any traps with moving parts. (Ref; IRC-3201.5 & UPC-1004.0) All of the aforementioned traps are strictly prohibited today.

The good news is that your existing barrel trap and no doubt the existing brass “tub waste & overflow” are made of heavy gage brass, not to mention that the pipes connecting it all are no doubt heavy wall DWV grade copper. If you carefully separate the copper from the brass and take it to your local metal scrap dealer you will probably recover enough money to pay for a new PVC or ABS P-trap & waste and overflow kit.

Also keep in mind that if your P-trap and waste & overflow will not be accessible once the tub is installed you will be required to install a glue-in type waste & overflow and P-trap instead of the common slip joint type. Personally I always install the glue-in type, then there is no slip joints that may potentially leak at a later date.

[Java_Bob]

Thanks, I knew you were going to say that I guess I will look for a copper trap adapter..

[LazyPup]

You can use a "Fernco" to make a code approved transition from PVC or ABS to the copper lines.

[Java_Bob]

Will do, Thanks LazyPup