New Tub Drain is Slooooww ?!

I have put in a new cast iron tub, replacing an old cast iron tub. In the process, I also cut out all the old CI 2" drian line. I replaced it all with 2" PVC. It is ran the same exact way the old drain line was run. I used a fernco no-hub to join the new PVC to the old CI pipe about 6" above the basement floor. Tub is on the first floor. The old tub did NOT have a vent, and I did NOT put a vent in this time either. This is likely why the original builders used a 2" pipe. There is no way to properly run a vent, and the old tub and drain did not have one, and it used to drain fine, fast.

But, now, for some reason, it drains like a dog - extremely slow. I use a garden hose run into the tub for testing, before I seal the tub in place with cement board and tile, I want to resolve this first.

I am just flat stumped with this. I installed the 2" PVC drain in the same place, the same exact way the old drain was. The only thing I can think that may be different, is not sure what size P trap they used before. I thought it was 2", and I used a 2" PVC P trap this time too. I then bushed it down to 1.5" to connect to the tailpiece of the tub drain.

Every where I read, people say to use 2" trap on a 2" drain, but now I am thinking maybe I should use a 1.5" trap?

Would the trap size make a difference in how slow the tub drains?

Again, for 50 years, the old tub drained perfect, and I put it all together the same way - but it drains so slow!?

Like I said, I am 75% sure the old drain had a 2" trap too, but maybe I'm wrong, maybe it was 1.5"?? The drain line itself is/was definatley 2" though.

SUGGESTIONS! Thanks in advance.

Waste and overflow

What type of waste and overflow assembly did you use on the new tub? If it is a lever-style stopper is it adjusted right? If not it could be partially blocking the drain even when the lever is in the open position. If you're using a toe-touch assembly they can slow the drain down. If it has a perforated cover over the drian hole it can slow things down as well.

cleveland1 said:

Every where I read, people say to use 2" trap on a 2" drain, but now I am thinking maybe I should use a 1.5" trap?

Would the trap size make a difference in how slow the tub drains?

Again, for 50 years, the old tub drained perfect, and I put it all together the same way - but it drains so slow!?

Click to expand...

A 1.5" trap would be a restriction between the tub and a 2" line, so no, that is not the problem. My guess is that your drain basket (or its strainer screen) in the new tub is the problem. Like yours, my new tub does not drain quite as quickly as the old one, and the only significant difference is the drain basket.

When you drain the tub do you hear water falling in the overflow plate area.

This sound is not always present, the sound varies with the length of the tailpiece to the trap, but if it is present it is an indicator of whether or, not the drain is keeping up with the waste & overflow.

It is entirely possible that while you were doing the work some junk dried out in the cast iron section of the drain and it is now partially clogged. I would have the cast iron section rodded to the main drain. Generally unvented lines will drain quite well unless there is a restriction.

I have taken the trip lever stopper out completely - first thing I did.

Today I will remove the perforated tub drain cover completely, and see if that does anything.

And I will also listen to the overflow tube for any sound.

This just does not make any sense. When testing with the hose, the tub accumulates about 2-3 inches of water, where it pretty much stays at that level the whole time during testing.

I already put my manual snake (about 5 feet) down the main cast iron floor drain in the basement, and there was nothing. Plus when I stuck the hose directly inside the 2" trap, before I set and connected the tub, it drained fine, no water backed up or spilled out.

This has got me stumped, and at a stand still!

If it drains fine without the grid strainer on, it is probably air-locked...
get a grid strainer with bigger holes...

Well... I took the strainer/drain cover off, and no change. However, I started to think that the garden hose (using for testing) had a pretty high rate of water flow. I had it hooked up to the utlity sink in the basement.

So, I timed how long it took to fill a 5 gallon bucket with the hose, and it took only 40 seconds! Thats more than twice as fast as a 2.5 GPM shower head.

So then I bought a 1/2" F/F hose adapter, and connected the new shower head directly to the hose, and tested the tub this way. Now, the draining kept up just fine!

Turns out, the drain just could not keep up with the raw hose rate of about 7.5 GPM.

To think I wasted a whole weekend on this suppossed problem! I even ripped out my entire new PVC drain this weekend, and replaced it with a steeper sloping thinking that was the issue!!! DUH !!!

Oh well - on to the tiling next weekend.

Thanks all.