Air pressure in the room

Hi all, first-time poster. I glanced through a search but didn't find anything specific to this issue; I hope I'm not repeating anything. A brief explanation:

My fiancee and I own a split-level with one full and one 3/4 bath on the upper level and one half bath in the lower level. We've been slowly working on renovating the lower level, so we've had a couple of rooms sealed off with painter's tape for over a month (lots of sanding of paneling, so we figured we'd try to keep them as clean as possible). I know little to nothing about plumbing -- I've replaced flush handles and know the minimum one learns from buying a house with a septic, but that's about it.

Halloween night I happened to be strolling across our front lawn and thought I caught a whiff of sewage. Distressing, as there's no sewer on our street and, to boot, our septic is under the front lawn. It seemed to go away after I noticed the master bath toilet running (the chain gets caught from time to time), so I figured perhaps it vents gas when water's running or something and forgot about it.

A couple of days ago, my fiancee mentioned she thought she smelled sewage as well, but inside the house -- outside the door of the lower half bath (that's been completely sealed off with painter's tape for some time). I'd been worrying about the lack of heat in there anyway, with the falling temps here in New England, so I figured I'd break the tape and get the heat on in there a bit and investigate a possible odor. The smell was pretty powerful. The bowl was empty but for a few ounces of water in the bottom, some backed-up sludge, and some flies. I flushed twice, which took care of both the latter items, and the system seemed to be OK.

My guess here is that there's something to having some available air pressure in the room for plumbing, and over a month of flushing the other two toilets has been slowly sucking the water out of this one to the point where the septic has backed up into it a bit. Can anyone with some plumbing knowledge confirm or deny this? I'm loathe to think there's something bigger here than just needing to air that room out, give it a good cleaning, and never EVER seal off a bathroom again, but I'd like to know for sure.

Thanks in advance if anyone has any information, it's much appreciated.

If the level of the water in the toilet drops far enough, or the traps in the other lines get too dry, the water normally in the trap will no longer be there to block a direct path to the sewage system. You should dump some water down each fixture. If you cap the lines, then it isn't a problem, but if they are open it is. this is normal. The traps are designed to do just that "trap" water to act as a seal from sewer gasses escaping.

It could just be from evaporation. My mother almost had the same problem as she didn't use an upstairs bath for 3 weeks. We KNOW the venting is OK on her house, yet the water in the bowl was down significantly.

Nate R said:

It could just be from evaporation. My mother almost had the same problem as she didn't use an upstairs bath for 3 weeks. We KNOW the venting is OK on her house, yet the water in the bowl was down significantly.

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Could that result in a small amount of waste in the bottom of the "drain" (for lack of a better term), though?

Home improvement can put a lot of dirt in the air...could it just be the result of that accumulating over the month or so?

jadnashua said:

Home improvement can put a lot of dirt in the air...could it just be the result of that accumulating over the month or so?

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No, unfortunately. It's been more "not sanding" than "sanding" and, as I said, we'd sealed the edges of the door off with painter's tape. There's also the overwhelming sewage odor when I opened the door; or would that just be from not enough water in the trap as you'd alluded to earlier?

(the trap is the hairpin elbow pipe that carries waste out of the bowl when flushed, right?)

denonymous said:

(the trap is the hairpin elbow pipe that carries waste out of the bowl when flushed, right?)

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The trap is the low spot in the bowl of the toilet.

If there is water high enough to cover the outlet hole that you can see in the bottom of the toilet, then it is sealed against sewer gas.

The stink could be coming from a trap in the tub, shower, or sink. Ventilate the room and then poke your nose around the overflow in the sink, and run some water in the shower and sink.

You can't seal a room with tape and plastic enough to maintain pressure across the plastic.

Outside sewer smells often come from the "modern" elevated leach fields that have large sewer pipes coming out of the ground. If your neighborhood has systems with vent pipes coming out of the ground, usually with a couple of elbows, that may be the source of sewage smell.

Bob NH said:

The trap is the low spot in the bowl of the toilet.

If there is water high enough to cover the outlet hole that you can see in the bottom of the toilet, then it is sealed against sewer gas.

The stink could be coming from a trap in the tub, shower, or sink. Ventilate the room and then poke your nose around the overflow in the sink, and run some water in the shower and sink.

You can't seal a room with tape and plastic enough to maintain pressure across the plastic.

Outside sewer smells often come from the "modern" elevated leach fields that have large sewer pipes coming out of the ground. If your neighborhood has systems with vent pipes coming out of the ground, usually with a couple of elbows, that may be the source of sewage smell.

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Yeah, there's no way this smell came from outside. It's possible it could be the sink, but the correlation with the lack of water in the toilet seems far less than coincidental.

Given the fact that there was, indeed, not enough water to cover the outlet hole in the toilet, it sounds like that's exactly where the smell came from. I now understand why you fill an unused toilet with molasses after draining it!

Now I'd just like to figure out how the bowl emptied of water and how some sludge made its way back in; that's why I originally thought it might be related to air pressure.

I would not use molasses.

The customary product is propylene glycol, sometimes referred to as "RV Antifreeze".

Another possibility is to put in a strong solution of calcium chloride. The toilet is china and will not corrode, calcium chloride is hygroscopic so it will retard evaporation, and in high concentrations it will even absorb water from the atmosphere.

Do not use calcium chloride if you have cast iron waste lines, unless you flush it with lots of water when finished.

Calcium chloride is the salt that is used in some of the higher priced ice-melt products.

Taps, when not renewed, lose water to evaporation - that is all that happened...
Pour some water in the bowl, and in any other drains in the room...
The "sludge" might have been some mold that grew in the "stagnant" water in the bowl while it sat...
RV antifreeze is the best solution to use as has been mentioned...

Bob NH said:

I would not use molasses.

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The situation of which I speak was at our place on Winnipesaukee probably 20 years ago. I'm not surprised things have changed since then.