Septin tank air intake

I have a septic tank in my house in Spain.

All the 110mm PVC toilet soil pipes drain into the tank.

Additionally, there is one 110 mm PVC pipe that collects rain water that also drains into the tank.

This is not good because it interferes with the proper working of the septic tank and it wastes rain water (it also has the added problem of flooding the septic tank)

I am thinking of cutting that rain water pipe, sealing the end that goes to the septic tank and diverting the other end into a water reservoir where the rainfall of all the other roofs of the house is collected.

The problem with this is that I wonder if I will be interfering with the proper ventilation and pressure equalization of the soil pipes and septic tank.

The septic tank needs air, that was provided by that rain pipe. If I seal it, I may stop the septic tank from working properly. If I don't seal it, since the cut will be inside a basement, I wonder if the basement will get bad smell and insects.

Also, since each toilet soil pipe has a water trap, will the soil pipes work properly if the whole system is sealed (i.e. no air entering at any point)

Thanks,

Antonio

Reply to
asalcedo
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Diconnect the rainwater pipe from the gutter at roof level, put a screen on it to prevent birds nesting, and run a new pipe down the wall from the existing gutter connection point, connecting it to the existing rainwater collection system.

And yes, a septic tank system will need venting to outside the buildng. If you vent it into a basement, the methane generated by the septic tank will gather in the cellar and may be at risk of causing a fire, or possibly an explosion.

Reply to
John Williamson

Hi John,

The roof is flat, draining in its centre through a pipe that runs internally in the house. Running a new pipe is not possible without major works.

I can vent the septic tank through an outside wall, but that is far from ideal since there would be windows nearby...

Many thanks.

Antonio

Reply to
asalcedo

Major works or not, I think you've got to have a vent to your soil pipe above - in your case - the flat roof level. If it's a flat roof used as a social area then I guess it needs to be even higher than that if you don't want to be anti-social. I once had a property with cesspool drainage and proper venting was essential.

HTH

Nick

Reply to
Nick Odell

Septic tanks need to vent somewhere. I don't think they specifically _need_ air (digestion of the waste is anaerobic, beneath a crust of semi-solid matter), but they generate gas (methane, mostly), and any water/waste entering the tank also displaces its own volume of gas. That gas has to escape or pressure will build up in the tank and connecting pipes, and force smelly gas up through the water traps on the toilet, wash basins etc. into the house. I agree it's not a good idea to have rain water also going into the septic tank, and disconnecting and sealing the vent to the roof, and diverting the rainwater makes sense. Is there any way you can install a vent actually on the septic tank itself?

Reply to
Chris Hogg

Okay.... So you'll need to extend the rainwater pipe to drain externally or connect to your rainwater collection system, whichever you prefer.

It needs venting to the exterior. However, if the vent is outside, the gases generated will disperse quite quickly, though it's recommended here that the vent extends above roof level. I don't know your local rules, but there may be a minimum distance laid down between the vent to the nearest opening window or door.

*Do not vent it internally*. Methane is heavier than air, will gather in the cellar, and may reach a concentration which will (a) suffocate anyone entering, and/or (b) explode if there is a spark from a switch.
Reply to
John Williamson

Sorry to reply to myself (said to be bad form on usenet, can't think why though), but it's just occurred to me that you can get rain water diverters for filling water butts etc that are fitted in-line with down pipes from gutters. Google for rainwater diverter. If you fitted one of these to your down/vent pipe you could divert the rainwater to a separate drain outside. Whether it would cope with a cloudburst I don't know, and it would probably need debris such as leaves clearing out from time to time, but better than nothing.

Reply to
Chris Hogg

In article , John Williamson writes

Methane is lighter than air. Butane and propane are heavier though.

Reply to
fred

Err no, not after the septic tank has reached a steady state. Any water entering the tank displaces its own volume of water which exits via the outfall and from there into the rest of the septic tank system, either the drain field or the anaerobic waste water finisher if it is a two-chamber design. The gas volume above the water stays more or less constant. What causes methane to leave the tank is the generation of more methane.

Reply to
Steve Firth

Well yes OK, my wording was poor. What I meant was there would be a temporary displacement of gas and a pressure surge when for example a loo is flushed or a bath emptied, before the 'clean' water exits via the overflow and drainage field. The outflow isn't simultaneous with the inflow into the system, at least not in my tank which is some twenty yards from the house.

Reply to
Chris Hogg

The septic tank at our last house had a metal vent about 6 inches tall next to the tank itself.

Mike

Reply to
MuddyMike

The septic tank is located in the lowest point of the house with truck access. It is also surrounded by bedrooms. Venting the tank there is not a good option.

Reply to
asalcedo

Divert the rainwater flow at the bottom, and vent the septic tank through a length of garden hose running *inside* the downpipe all the way up to the roof? Co-axial bodge should be feasible with some adaptor bosses and a tube of silicone sealant.

Reply to
Steve Walker

Hi Steve,

I had thought of the same thing but will a 1" diameter garden hose be enough to vent? It certainly looks like it will leave enough space in the 110mm pipe to drain properly, especially because the garden hose will go only vertically.

It is easy to do. Drill a hole in the 110mm PVC, place a boss adaptor on it and run inside the hose.

Being design for pressure, garden hoses are relatively thick walled. Good quality electrical corrugated conduit offers more internal diameter for the same external one with the added advantage of being easier to run along bends.

Anything bigger than 1" is probably out of the question because it will likely lead to clogging.

Reply to
asalcedo

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