Basement bath clogs: vent vs backwater valve?

Old 09-16-16, 08:20 AM
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Basement bath clogs: vent vs backwater valve?

We have a 14 year-old house with original basement bathroom with sink, toilet, bathtub. They are in that order of drainage, and connect under the foundation to common drain and backwater valve

-Over the 2 years we've had the house, the basement toilet has occasionally clogged (could always clear with plunger)

-was infrequently used (by guests), and sometimes I would find the toilet water level very low in the bowl.

-Recently (with guests) has been flushing slow and clogging more frequently.

-When shower would run, it would suck water level down in toilet bowel and then suck air IN through the toilet.
I thought it might be a problem with the vent pipe (if vent pipe blocked, then shower drain is compensating by sucking air through toilet?)

-2 weeks ago, had a clog in the toilet. When I plunged it, I could hear gurgling in the shower drain (first time that ever happened). When I turned on the showed, I got bubbles OUT of the toilet (also first time)- so I thought the clog was now in the common drain for the toilet/shower. I closed the bath plug, and sealed off the bath overflow (duct tape) and plunged again. When I was first plunging, I could see the duct tape bowing out (positive pressure in pipes- makes sense with clog). Then, there was big sucking sound (duct tape also sucked in) and the clog cleared. The toilet flushed perfectly. Then, when I turned the shower on, it went back to sucking water the toilet down and taking air IN through toilet (no more bubbling out).

My thought was that a problem in the vent pipe was predisposing it to slow flush/clogs. When not clogged, the shower would suck water/air OUT of toilet (poor venting). When clogged, it would push air INTO toilet (clogged drain line filling up with water)

We had a plumber come out this week and it was clogged at the time (air bubbling OUT of toilet, when shower is on). He said no way that the problem was the vent pipe (everything else in the house drains fine). I thought it could be the vent pipe connection BETWEEN the basement bathroom and the rest of the house (it takes a 90deg turn above the basement bathroom to connect somewhere in the middle of the house), but he said that was as likely as “being struck by lightning”.

He suspected the backwater valve for our basement bathroom, and said he sees the flappers fail/clog in houses ~10 years old. Unfortunately, the BW valve access sleeve through the foundation was not centered over the access plug for the backwater valve, so half of the valve access plug has concrete over it.

In short, no way to check it without cutting into the foundation to check and then replace the BW valve. Quote $2000 (cut hole in foundation, check BW valve, replace if faulty, re-concrete with now corrected sleeve). 2nd opinion coming out today.

Does this make sense? Fair price?

To me, BW valve makes sense for location of current clog, but- before the clog- wouldn’t have this been a venting problem?
(air sucking through toilet with shower use)

Definitely appreciate any help!
Old 09-16-16, 10:19 AM
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It certainly sounds like there is a venting problem. But without knowing exactly how and where the vent is connected with respect to the fixtures it's hard to be certain. For example, if the vent goes first to the sink and the rest of the fixtures are wet vented through that drain, then a blockage in the drain can also cause venting problems because water backed up in the drain blocks the venting action of downstream fixtures. That's why wet venting is no longer good practice.

Even if each fixture has it's own vent connection, a backup in the drain can plug up one of the vent connections.

If you have access or cleanouts, you can certainly try flushing or snaking the vents, but I suspect you are going to end up fixing the backwater valve problem and going from there.
Old 09-16-16, 10:35 AM
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Most of your issues point to a persistent clog. Usually this would point to a collapsed pipe or root infiltration, but in your case, with a backwater valve, that's the likely culprit.

I'd ask him what the price would be if he opens up the concrete and finds it's just clogged and doesn't need replacing. That said, being 10 years old, it may just be worth the replacement.

I can't comment on the price since pricing varies so much based on location. You'll know better once you get the 2nd quote.

Let us know how it goes!
Old 09-20-16, 09:27 PM
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Thanks so much for the replies- I really appreciate it.

I think the tub/toilet may be a wet vent as you thought(pics below).

The second plumber also agreed that the primary problem is likely the BW valve, and that vent blockage alone would be very uncommon with a 3" vent stack.

2nd plumber recommended cutting down to the BW valve, clearing the clog, and repairing the valve (new valve flap only) for $1000.

(again, 1st plumber recommended replacing it with a new valve for $2000.)

Of course, I'd prefer the repair for 1/2 the price of replacement.

Any reason that repair of the current would be a bad idea?

Both plumbers are offering a 1 year warranty on the work. I imagine if the repaired valve fails again (and does require replacement), it would likely be in the first year. At least with the access sleeve fixed, the valve would be accessible for future repairs.

Offset access sleeve
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Behind toilet (sink to right, tub to left)
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Showing tub drain to the left of toilet/sink
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Vent pipe above prior pics
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Old 09-21-16, 06:09 AM
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IIWM, I'd go the repair route. It may be that when the concrete is opened and the valve is accessible that it becomes clear that replacement is advisable...but at least your plumber isn't starting with that mindset. Just makes sure that however the concrete is repaired it allows for future access/replacement if needed.

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