I hope the gas kills the cockies!

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    • #279869
      Rog Davis


      I’ve had a few problems with the plumbing in my house over the years, but the problem I encountered last night is the worst yet.

      To save a long description I’ve roughed out a sketch of the house, with the layout of the wastepipes and bathrooms, etc. The sketch is here:


      We started smelling a strong smell of gas (similar to petrol or paint) in the top bathroom and the bottom bathroom and kitchen, at the same time. There was no such smell in the middle bathroom or toilet. The property is on an incline, so the top bathroom is higher.

      1) The smell wasn’t sewer gas. It smells like petrol or paint.

      2) This is an electric house – no gas lines anywhere.

      3) All the traps are full of water, and there are no pipe blockages anywhere.

      4) There is an induct vent about chest height on the lower kitchen, higher than all the other traps and drains in that kitchen and bathroom.

      One plumber told me it might be a neighbour using petrol or chemicals and maybe a cloud of this gas might have been sucked into the induct vent, but actually no neighbours were doing this, and anyway, we couldn’t smell anything outside. The smell is only inside the top bathroom and the bottom kitchen, and some in the bottom bathroom.

      I could not find a vent for the top and middle bathrooms, or the toilet on the left side of the house. Unless they’re hidden I can’t any. There is an open external ground level drain hole between the top and middle bathrooms, but this isn’t really a vent, and we could smell no gas in it.

      I thought that maybe the external induct vent next to the bottom kitchen (close to where the worst smell was in the bottom kitchen) might have stopped working. Maybe it was blocked and this would allow methane gas to build up inside the pipes. I seem to remember that methane gas can work its way through water, and thus get through traps. Is that right?

      Anyway, I could not unscrew the induct vent from its vertical pvc pipe, so I cut it off with a hacksaw. I also unscrewed an elbow on the drain coming out of the kitchen wall, to let the gas out of these two holes. The gas was very strong in both.

      Meantime in the top bathroom I opened a window and put the ceiling fan on, since there are no access points there to open up.

      An hour later and the top bathroom still stinks of gas but the bottom kitchen and bathroom are not so smelly.

      My questions are these:

      1) Does it sound like the induct vent was blocked?

      2) Do induct vents (that only let air in, not out) often clog up? I couldn’t see much in the way of clogging – just a few small dead insects in there.

      3) Is there an induct vent (in Australia) that can be removed by hand so that if this happens again I won’t have to cut the pipe and make it shorter each time?

      4) Could this problem have been caused by something else?

      5) Why are there no vents on the top bathrooms and toilet? Aren’t they supposed to be part of the building codes? We haven’t had any smells like this for years now, so how did the system function without vents all this time?

      6) Can methane ‘move’ through traps like that? I can’t see any bubbles coming up, yet it’s definately getting in.

      Separate problem

      If you look at the diagram you’ll see that in our top bathroom the toilet, shower and sink are all connected by a triangle arrangement, and there is a drain hole in the floor where all these pipes meet before going away and around the house. We get cockroaches coming up through the shower and through the floor drain, and I think sometimes through the sink. For a long time I couldn’t understand why. Eventually a plumber told me it was because this arrangement was actually illegal now, because when you flush the toilet, suction caused can suck some water out of the traps in the shower and sink, and thus let the roaches in. I’d like to shoot the idiot that built this place.

      So after that we had to run the shower and the sink tap every time we flushed the toilet in order to make sure the traps were full, and keep cockroaches at bay.

      Obviously we could have a plumber rip up the whole floor and replace the entire bathroom in order to fix this, but that will cost many thousands of dollars. Is there any other solution?

      I’ve been offered three solutions by plumbers so far on this, and neither worked. The first was to pour 4 litres of petrol down the shower drain. Well that failed. The second was to pour this stuff that allowed some ‘friendly’ bacteria or fungus to grow down there, which would remove the smell that attracts cockies. That failed. The third charged me $160 to put in two plastic floor drain grates in the two top bathrooms, which had a sifting device that was filled with fine sand. These would still allow water to drain but would stop cockies getting in. The cockies simply continued coming up through the shower and sink.

      On the bright side, maybe this wretched gas killed some cockies. Lord knows, nothing else would.

      Thanks in advance for any replies to these two problems.


    • #301872

      Sorry – I messed that link up to the graphic. Here is the address:


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