Wireless septic tank - how to transmit the transmitter signal from the manhole

Hello to all the specialists present on this forum. I am a complete greenhorn so I humbly ask one question in the hope that the answer in the language of a normal person will be easy. I have this idea of installing a wireless septic tank sensor. All sensors I have found require that a radio transmitter is placed outside the sump to send an overflow signal to the receiver. Unfortunately, this solution is not very suitable because my septic tank is located in a residential street leading to garages of detached houses. So car traffic and the activities of the neighbours (e.g. snow ploughing) could harm either the transmitter or a possible cable connected to the transmitter. In addition, sensor manufacturers recommend not to mount the transmitter in a manhole because in the case of a metal cover the transmitter signal only has a range of a few metres, which in my case is insufficient. My question: if I want to install a transmitter in a septic tank manhole, is it possible to transmit a radio signal over a distance of e.g. up to 10 m? Thank you in advance for any advice.

It's a tough topic mate - whatever you mount there, it needs to have its own power supply and be able to withstand high humidity/over 90% non-stop/. On top of this, there is also the acidification of this atmosphere caused by the presence of hydrogen sulphide.

Hello, thanks for your reply. I agree that this transmitter has to be able to withstand harsh conditions and it seems to me that it can be done if the transmitter is well protected. I am thinking of putting the transmitter in a sealed box to protect it from moisture and vapour. At the same time there is still the question of how to transmit the radio signal. I don't need a constant signal or just a short pulse to the receiver, like with a garage door. Is it possible to lead a cable from the transmitter to the outside which can be used as an antenna? Or is it possible to replace the metal cap with a cover made of another material? Thank you in advance for any suggestions.

If the cover is metal without any holes it is in practice an insurmountable barrier for the radio signal.
Is there a lot of traffic on the road ? Can anything be attached to the cover ?
You have probably seen the reflectors commonly known as cat's eyes hanging on the asphalt. The casing is about 25mm thick and can withstand a little car traffic. A transmitter with a battery can be placed in such a piece. The whole thing, of course, has to be encased in resin. I have been testing the durability of such a solution for a parking space occupancy sensor for three months. Unfortunately, there has hardly been any snow this year. So it is difficult for me to say whether snow and ice will cause connectivity problems.

Thanks to TvWidzget for your willingness to help. The cover has two holes, about 3 cm in diameter, for ventilation I think. Do you think it will be enough to transmit the signal?
Your solution is not bad and may be a solution in my case, especially since the car traffic is very small. Regarding ice or snow, I think that a few to several centimetres of snow/ice is not a problem for radio waves - if we take the example of a garage door remote control where the signal goes through the wall. But I agree that it is better to test during a real winter.
Speaking of winter and your sensor, did the battery prewarm the low temperatures?

The 14250 lithium battery can operate over a very wide temperature range. It can withstand even -40st.
As far as the penetration of radio waves through water is concerned, even a millimetre can be a problem. However, if the sensor periodically sends its status it will reach the receiver sooner or later. A septic tank does not suddenly overflow, after all.
If you place the antenna in the gust hole and the receiver is above it, e.g. on a lamppost, you may be able to receive the signal. However, you are probably thinking of a transmitter on 433MHz. In this band the antenna is quite large. Any conductive elements near it will significantly reduce the amount of energy emitted.

cerga wrote:

The cover has two openings of approx. 3 cm diameter, for ventilation purposes I guess.

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Rather for hooks to lift the cover.

gimak wrote:

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Rather on hooks to lift the lid.

Thank you gimak for the explanation. I will not hide that I am surprised if these holes are only for lifting the lid because in this case I start to have various other ideas.
Sometimes I have noticed tubes glued to the covers, something like chimneys and that is why I thought that these holes are for ventilation.

TvWidget wrote:

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The 14250 lithium battery can operate over a very wide temperature range. It can withstand as low as -40st.

Cool, thanks for the information, I will take it into account when designing the prototype .

In your case where and how far is the receiver located?

On another subject: is there any material readily available (plastic?) and hard enough to transmit the signal? After the reply of my colleague "gimak", I am beginning to think about replacing the metal cover with my own, made of this material.

Thank you and best regards.

I was referring to such an enclosure:
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The receiver at my place is just high up, but this is due to the specifics of the application. I have not measured the range. I think it will be 10-20m. The transmitter sticks out above ground level. The receiver can therefore also be placed low.

Thank you for your suggestions. Right, if there is a "closed circuit" it is possible to estimate from the water meter how much water is in the septic tank. At the same time, when using tap water for garden irrigation, this circuit is not so closed and without a water meter for the irrigation system it will be difficult to estimate the amount of water poured into the septic tank. Hence the need to measure the level directly in the tank.

This solution is possible, but unfortunately not very reliable> a manhole flap is not watertight. Water from the street can always get in there - and that's the end of measurements. Can you draw a side cross-section of this septic tank, my friend? Some simple drawing, and give the approximate diameter of the waste pipe. I ask because I think I have an idea about your prabol.

kot mirmur wrote:

Are you able to draw a side cross-section of this septic tank, fellow author? Some simple drawing, and give the approximate diameter of the effluent pipe.

Hello, I will provide pictures. One with the lid and one without (sorry for the views). The lid is 54 cm in diameter.
Unfortunately the diameter of the drain pipe unknown because, as can be seen in the photo, the pipe is hidden somewhere under the sump.
Without diving it is not possible to measure .