How replace drain to sewer connection.


New member
Nov 24, 2014
Huntington Beach
The P-trap on our pool drain rusted through (cast iron). It lasted almost 40 years, not bad I guess. I would like to replace with 3” ABS and have a few questions.

1. I could buy a new 3” “Cast Iron” P-trap and replace. The Cast Iron is not as wide as the ABS, so this would be a quick and easy fix (see photo). The problem is I don’t like how the old cast iron “T” looks – where the P-trap connects. The Old “T” and P-trap has five Fernco fittings holding everything together. They worked well but look bad.

2. In order to install the 3” ABS I need to remove the Cast Iron “T” and use a Fernco fitting to connect a ABS “T” to the house sewer line to start the ABS pipe, then I will have the room I need. (An ABS P-trap is a lot wider than a Cast P-trap). Also, I will stay with the same set-up as in the photos but just use ABS and one Fernco fitting. The ABS P-trap will not fit in the desired space because the Cast Iron “T” side pipe sticks out to far.

I thought about coming out of the house sewer line with a 90 curve, but decide that they used a “T” so that it laid flat in the dirt so it would be more stable.

3. Also the cast iron drain stand has a split in the side. I will replace with a 3” ABS. This old cast iron pipe tapers from an opening of 5.75 inches to 3 inches. I can only find an ABS reducer from 4 inches to 3 inches. Do they make anything in ABS like the old Cast Iron one? Also can I find a drain grate to fit inside, to protect to sewer line.

Any input and guidance would be appreciated.



TFP Guide
Jun 4, 2012
western NY
Technically, you have an "S" trap, not a "P" trap. An "S" trap has been non code compliant in most areas of the country for several years now due to the fact they are seldom vented properly (such as yours). The lack of proper venting leads to the ability for the trap to be sucked dry.

Here is a link showing this on a laundry drain setup(similar to yours) and the proper methods to do a proper install.