Toilet plumbing question

[fisher83]

What would cause the water level to drop in a toilet bowl within a few minutes of flushing? This only happens with my basement toilet. The other two on my main floor and upstairs are also new and they work great. I don't see any leaks anywhere, the tank fills fine and the bowl gets to a normal level but just doesn't stay there more than a few minutes before dropping significantly. The old toilet that was in there also behaved similarly.

 

[JHZR2]

Some sort of pressure imbalance that causes a bit of suction on the water level. It steals just a bit and everything else is static, so…

 

[PimTac]

You might want to check the vent stack.

 

[MParr]

Get a quart of water and pour into the bowl. Don’t pour it fast or directly over the trap. Pour it in on the side of the bowl, Watch the water level. Does it fall and settle at a fixed point? If so, it may be settling to the desired level. It could be that your fill valve is overfilling the bowl. Keep an eye on it. See what the water level does over a 12 hour period.

 

[fisher83]

Going to check the vent tomorrow. I'm also going to try your suggestion about slowly adding some water and will check the level in the morning.

 

[Lubener]

Going to check the vent tomorrow. I'm also going to try your suggestion about slowly adding some water and will check the level in the morning.

I would think if the vent stack had issues, the toilet would not flush completely and would also affect the other toilets in the house. Let us know what you find.

 

[PandaBear]

This seems to happen a lot when the toilet has a restriction, it seems like somehow with capillary action of the congestion or some vacuum of the restriction is slowly pulling something away. Typically once I unclog the whole thing this would go away.

 

[CharBaby]

My basement toilet started to do this EXACTLY after 30 years. After I would flush the toilet and the bowl & tank would fill, I'd wash my hands at the sink and the water level in the bowl would drop right down to the hole. After 3 yrs, it has now stopped doing this but NOW, I can hear it venting off of the sink.

 

[bugeye]

Cast iron vent pipe corroding internally limiting venting ?

 

[Lubener]

Cast iron vent pipe corroding internally limiting venting ?

If anything something like a dead critter or a bird's nest falling down in.

 

[MasterSolenoid]

Some sort of pressure imbalance that causes a bit of suction on the water level. It steals just a bit and everything else is static, so…

I have noticed many times the water level in toilet bowl will go down (1 inch) on windy days.

 

[opus1]

I have noticed many times the water level in toilet will go down (1 inch) on windy days.

I've noticed the water in the toilet nearest the vent stack moving around on windy days, and have also seen the level drop due to that.

OP's problem sure sounds like a venting issue. Note: I am not a professional plumber, I do not play one on TV, nor did I sleep at a Holiday Inn Express last night.

 

[dbias]

When flushing does the water rise higher than the other two and take longer than usual to empty the bowl? I've seen this on toilets that have a slight clog. The slight clog narrows down the diameter of the pipe thereby killing the free air space for water and solids to pass creating a suction that empties the bowel. Plung the heck out of it or run a snake in it to clear it. I've also seen this type of a restriction caused by flushing dental floss and over time it builds up by laying over the highest point of the trap in the toilet itself causing a restriction.

 

[fisher83]

I got up on the roof today and did not find any obstructions in the vent but I went ahead and hosed it out anyway. All other water appliances are operating properly. Toilet bowl still fills to normal level then drops down within a few minutes. If I just slowly add some water to the bowl the same happens as well. It wouldn't surprise me if something in this bathroom was never plumbed right in the first place when this basement area was finished by the previous owner.

 

[PimTac]

I probably would not go any further unless the toilet has trouble flushing waste or sewer gas is obvious. If either of those are happening it might be worth pulling the toilet.

I assume this is on a concrete floor?

 

[fisher83]

Yes it is on a concrete floor. I put some main line drain cleaner down the floor drain and a similar product down the toilet in case maybe there is a minor obstruction somewhere. It flushes just fine and I can see the occasional bubble in the water which I assume is sewer gas but its staying below the water line. I thought I remembered the old toilet acting this way too but I could be mistaken. That bathroom got almost no use at all in 2020 since we really only utilize the basement when we have people over which we really didnt do last year. I'm certainly not counting out the possibility that I went wrong somewhere during the toilet installation. I don't see any leakage around the toilet but could a very minor leak in the wax ring cause the bowl to drain down a little and just not leak enough to see it seeping out around the toilet?

 

[Lubener]

I have noticed many times the water level in toilet bowl will go down (1 inch) on windy days.

Not uncommon under windy conditions.