Bathtub gurgles

[Master Brian]

My bathtub, which is a clawfoot tub - if that matters, gurgles when it drains. Is that normal? I can't recall if my other house's tub did this or not. Maybe a little, but this seems loud. It doesn't do this when anything else drains.

The tubs drain is 2" PVC, it T's into a vertical 4" vent/drain stack, which drops about 1-2' before going into the main 4" sewer line. Above the "T" is cast, below is PVC. From what I can figure out there is nothing else dumping into this 4" vertical pipe. So it only serves the tub's drain and vent. The cast terminates the roof.

Google searches seem to say gurgles are the result of a clogged vent, but they also seem to only talk about gurgling when trying to drain two fixtures at once.

So, I wonder, is this normal due to the water draining really quickly through the 2" line or do I need to look into having the 4" cast iron vent section snaked.

[Basement_Lurker]

You already picked up on that it might be because the water is draining too quickly. And since I am not there, and you describe your piping as definitely oversized, it makes sense that most likely the water is draining quickly enough to make a constant noise like a sink does...otherwise, if you are intermittent noises like bubbles coming up, then you probably have a clog.

[jimbo]

A clogged vent can cause OTHER fixtures on the line to gurgle, as their traps are siphoned, and a clogged drain can cause many symptoms.

In your case, I gather that slow draining is NOT your issue? And is there a trap close to the tub?

[Master Brian]

A clogged vent can cause OTHER fixtures on the line to gurgle, as their traps are siphoned, and a clogged drain can cause many symptoms.

In your case, I gather that slow draining is NOT your issue? And is there a trap close to the tub?

There is a trap about 12-18" under the floor below the tub. I wondered if it's too low, but there are other items obstructing it from being up further and it is basically horizontal, with slight slope to where it ties into the vertical drain/vent stack.

As Basement Lurker suggested it is probably just draining too quickly, as there are no bubbles and nothing else gurgles as it drains and it doesn't gurgle when anything else drains.

Is it actually possible for it to drain "too" quickly? There is one of those screw on cleanouts in the P-trap and water seems to be in there every time I check and I don't smell any odors.

Thanks for the replies...