Septic tank pumpout problems

Rod, if the septic tank effluent is discharged to the surface of the ground, from where is the water being siphoned? It seems to me that the only effluent that could be siphoned is that which remains in the pipe when the pump turns off. This is the same volume of effluent that would drain back through the hole in the pipe. That is, of course, if the discharge pipe grade is such that it allows the effluent to flow back to the tank.

Upon viewing your excellent diagram, it seems to me that your septic tank is exceptionally deep. It is difficult to determine the situation without a more complete description of the terrain around your home.

Additionally, it is a very dangerous threat to the public health and the environment to discharge septic tank effluent directly to the surface of the ground. If you live in the USA, this practice is prohibited.

Please describe in detail the type of float switch controlling the effluent pump, the volume of effluent in the discharge pipe, your general location in the world, and the terrain around your home. I will attempt to provide a solution to the problem.

Thank you for your reply, John.
I think I may have figured out the problem: I recently replaced the pump and the new pump has a mechanical lever type piggyback switch attached directly to the pump. Thus the effluent level need only rise around 6 or so inches before turning the pump on. What happens is that, yes, some of the effluent is ejected but what remains in the pipe (about 150ft of 1-1/2 pipe) flows back into the tank turning the pump back on again. This will continue for several pump cycles until enough effluent has been discharged that the pump switch is below it’s turn-on threshold. All it takes is another flush of the toilet to start the whole thing again. I’ve purchased a float-type piggyback switch which I will adjust to reduce the cycling.
I live just outside of Edmonton, Alberta, Canada and I suspect that, due to our long cold winters, the septic tank needs to be quite deep (up to 8ft frost depth here). As for the surface discharge, that was a concern for me and I had looked into it when I purchased the property. The county here indicated that surface discharge systems were still acceptable provided that it was an existing system and you lived on more that 9 acres. Any new construction would require a field or mound system.

One additional question, if I may: I took a close look at the hole in the PVC elbow and it really appears to have been drilled out on purpose. I am wondering if this is necessary for the pipe to drain back due to the U-turn at the top of the tank?

Thanks,
Rod

John. We dont suffer from frost depth over here, however, would the hole be for the dead water in the discharge line to drain out rather than freezing in the discharge pipe?
Bob

Rod,
>I am wondering if this is necessary for the pipe to drain back due to the U-turn at the top of the tank?<

The answer to that question is yes. The purpose of the “U-turn” in the pipe is so you can reach the union, which should be installed in the horizontal section of the pipe for ease in pulling the pump. Many older homebuilt systems do not have a union at this location. Without a union the technician maintaining the pump must cut the pipe to pull the pump. When the pump is reset, typically, a coupling is used to reconnect the pipes. Many DIY’ers are reticent to spend the $10 for the union.

I am still trying to figure out the hydraulics of this system.

>I recently replaced the pump and the new pump has a mechanical lever type piggyback switch attached directly to the pump.<

My question is at what elevation was the new pump placed? I presume that the old pump was controlled with an independent float switch which was tethered to the discharge pipe at the desired elevation. Typically, the pump rests on a flat rock, or perhaps a small concrete slab on the floor of the tank. The dose volume, and the drawdown elevation can be adjusted by either lengthening or shortening the cable. The liquid elevation ranges are determined by the attachment elevation of the float switch to the discharge pipe.

The elevations (turn on/turn off) on the systems that I install allow for about 200 US gallons to be discharged per cycle, and depending upon the size of the tank, the drawdown distance is 4 to 6 inches. In order to maintain the required 30 hours of hydraulic detention time in the tank, the tank outlet hole is capped, and the turn off elevation is set at the outlet invert elevation.

When you replaced the old pump with the pump controlled by the mechanical lever float switch, was the new pump placed on the floor of the tank? If it is on the floor, then the effluent entering the second compartment of the tank is the backflow from the discharge pipe, and the effluent coming around or under the center baffle from the first compartment of the tank, and the second compartment is almost empty when the pump turns off. Typically center baffles are not water tight.

In any event, by installing the independent float switch, and setting the elevation of the attachment so that the liquid elevation of the tank drops 4 to 6 inches, the problem should be solved. You can use the new pump with the mechanical lever switch, and connect the new float switch in series with the mechanical lever switch.

You mentioned the word “piggyback” in your response. I recommend that the electrical connections be hard wired, and placed in a waterproof underground electrical box located outside of the tank riser. The weak points in this type of system are the plug-in electrical connections. Corrosion of the plug prongs causes low voltage problems, and the pump motor burns out rapidly.

I will limit comment about the wisdom of the County allowing surface discharge of septic tank effluent to simply state that even grandfathers can fall ill from typhoid fever or cholera, and grandfathers can also cause significant environmental damage. Nuf’ said.

Bob,
>We dont suffer from frost depth over here, however, would the hole be for the dead water in the discharge line to drain out rather than freezing in the discharge pipe?<

The answer to this question is yes. Is there no frost in the Blue Mountains, or in Tasmania?

Now Bob, I have another question for you. I had the pleasure of visiting for a month your incredibly amazing and beautiful continent in 1999. I have read several books about Australia such as “The Fatal Shore” by Robert Hughes, “In a sunburned Country” by Bill Bryson, and several others. My favorite souvenir of my Australian adventure is my Akubra felt hat. It is the Coober Pedy model with an opal on the side of the hatband. I have long known of the incredible town of Coober Pedy in the State of South Australia. I understand that about half of the residences, and many business buildings in Coober Pedy are underground. My question is, how is sewage treatment handled in Coober Pedy?

John. In answer to your question about frost in the Blue Mountains & Tasmania- YES it does frost on most of southern Australia it even frosts in southern parts of Qld, However I believe that even in the Southern Snow Fields we haven’t a 8ft frost zone. Frost is usually over night & melts when the sun emmerges. I can remember when working in the Dorigo Mountains on the mid North Coast of NSW & having to drain above ground water pipes in case they froze. But not underground with 10″ cover. Never did like cold – thats why I moved to Bowen – on aprox same lat at Mexico but South to you.
To your question about Cooper Pedy – I dunno. I will attempt to find out though & post the answer.
Bob

Rod
The hole is for draining the lines to help keep them from freezing or to stop any siphon effect you may have. Put a 3/16” hole just beyond the 90 so it will point down in the pit. A hole in the 90 where you show it will create more of a wear opportunity for the water. The Wisconsin code at one time had some restrictions in it about the velocity in pipes because they did not want to wear out 90’s. It is true with a hole in the 90 as shown will wear more. If there is a check valve (you do not show one in your sketch), you will need one just above it to drain the water still in the loop. With no check valve, the water in the loop will drain back through the pump.