I have two plumbing questions I'm hoping someone here can help answer:

1. One of our toilets randomly clogged, and we don't know why. If we go a day or so without touching it, it will flush once or twice just like normal, but then the third time will back up with water, and then will slowly drain over the course of about 30 minutes. Kind of like there's a deep clog or something. I've plunged it to no avail.

2. On a different bathroom, if you turn on the faucet for a minute or so, air bubbles will come through the toilet a few feet away. We've never noticed bubbles otherwise, only when the nearby faucet is on for a minute or so. Fairly large bubbles, not like fizzing bubbles.

We do have cast iron pipes, so I'm hoping it's not that. We did have our home inspected a few months ago, and the inspector ran a camera and said he didn't see any major issues, but noted typical cast iron deterioration. Several of our neighbors have had their pipes replaced in recent years, however.

When I Google it, it looks like both could be related to a clogged vent, which I'm hoping it is, as that's a much cheaper repair.

DeLaHonta said:

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I have two plumbing questions I'm hoping someone here can help answer:

1. One of our toilets randomly clogged, and we don't know why. If we go a day or so without touching it, it will flush once or twice just like normal, but then the third time will back up with water, and then will slowly drain over the course of about 30 minutes. Kind of like there's a deep clog or something. I've plunged it to no avail.

2. On a different bathroom, if you turn on the faucet for a minute or so, air bubbles will come through the toilet a few feet away. We've never noticed bubbles otherwise, only when the nearby faucet is on for a minute or so. Fairly large bubbles, not like fizzing bubbles.

We do have cast iron pipes, so I'm hoping it's not that. We did have our home inspected a few months ago, and the inspector ran a camera and said he didn't see any major issues, but noted typical cast iron deterioration. Several of our neighbors have had their pipes replaced in recent years, however.

When I Google it, it looks like both could be related to a clogged vent, which I'm hoping it is, as that's a much cheaper repair.

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Have you gone into the attic to see if the vents for those two toilets connect before they leave the roof?

Can you pull the one toilet that clogs and just pour water down the drain and see how fast it back up (or if it does). If it does not, then it sounds like a vent issue (because now the open toilet drain is venting). Leave that toilet off and run the sink in the other bathroom and see if you get the air bubbles in the second toiler? If not then that open toilet is acting as the vent for the system and for sure it's a clogged vent line and the two systems are connected somewhere in the attic.

The toilets are on opposite sides of the house and do not share a connected vent pipe.

These two toilets were recently replaced by our contractor, whereas all other toilets (which we have noticed no problems for) have not. They did stuff a bunch of stuff in the hole when they were replacing tile to prevent the smell/sewer gas, so I'm wondering if they just stuffed that down instead of removing it and it's blocking a vent pipe.

Pull each toilet and see if you can pour a gallon of water down the drain with out it gurgling or backing up.
When you pull the toilet, the drain line is now vented (the toilet U-Bend is your trap on the toilet waste line - like the P-trap on your sinks).

If it backs up, its not a vent problem but a blockage somewhere. With the toilet removed, it's a lot easier to get a snake down the line to find the blockage.

EDIT: Just remembered I had a similar problem to your toilet 1 after a new install. Turns out I did not use a tall enough wax ring to account for the tile, grout, etc. and the toilet was actually leaking/venting at the wax ring, vapor locking and into my garage below (but not enough to notice right away). New, higher wax ring, problem gone.

EDIT 2: When I pulled the toilet, it drained just fine when I poured water, and I thought I had a broken drain line so I cut out the ceiling in the garage (no knowing it was leaking - which was nice when I cut out that 1'x1' section of ceiling) and was like "WTF" when I got some nice water dumped on me. The pipe was fine. I had my son flush the toilet and water came spraying out everywhere. Then I looked at the bottom of the toilet and saw there was no evidence the wax ring was physically touching the bottom of the toilet.

When we had this issue it was a couple blockages that had built up in our sewer lines. They would slowly drain out but when filled faster than they could drain, would back up to whatever fed into them.

I used a couple of different types of snakes and one of those expanding line pressure hose fittings to blast the lines out and had to repair one break I found but after that, no problems. Sometimes soap scum or oily deposits or hair can build up and cause a backup.

MouthBQ98 said:

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When we had this issue it was a couple blockages that had built up in our sewer lines. They would slowly drain out but when filled faster than they could drain, would back up to whatever fed into them.

I used a couple of different types of snakes and one of those expanding line pressure hose fittings to blast the lines out and had to repair one break I found but after that, no problems. Sometimes soap scum or oily deposits or hair can build up and cause a backup.

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I had that at my kitchen sink b/c the main line had a clog going out of the house. It was grease, soap scum, etc. that just clogged the line. But all my toilets flushed just fine b/c they were far enough away.

But it was a problem that slowly got worse, not all at once thing that seems to be going on with the OP

OK, another one (30+ years of home ownership!)

Had an AC pan drain going to a sink that clogged up a shower drain that combined with a sink that had the AC pan drain pigtailed into it. Learned I needed to flush those AC unit drains with a water/bleach mixture 2x a year to keep the algae/growth out of the lines.