crooksey

What was the proposal for waste and rain water in the planning documents? Usually this has already been specified. Probably easier and cheaper for a treatment plant and soakaway (if soil allows).

If you vent at the tank, just add a very good AAV valve, its not that noisy and its only 2x per day for 30mins. If you set it to empty at 8am and 8pm you will likely never hear it. Ideally use a black stand pipe and a black AAV and hide it best you can. The lids are not airtight anyway so will self vent.

Usually on a one2clean, I vent after the tank and before the drainfield. The way in which the blower pipes feed to the control box can also be put in 110mm and an auxiliary vent can be added (although this will be noisy during discharges).

The installation manual states that it must be on its own 16A MCB. However, I have installed these on a 13a fusespur with the largest 120 air compressor with no issue. If you have a gravity system the power draw is tiny, however if you have a pumped outlet, I would install on a 2.5mm 16a dedicated circuit as per the manual.

Just get a drainage company to seal the pipes from the inside with a patch liner.

The key to remember here is all to do with the winter water table level. If your tank is deep, there is a chance your drainage field could be below the level of the winter water table (therefore useless). If you have a pumped outlet, you can have the field 300mm below the finished ground level and remove any doubts about winter water table level. Or go gravity, and have an NRV on the drain-field and have an overflow tank, so that in the event your drainage field is under-water, the outlet of the PTP goes into an ancillary tank, that can then be pumped out whenever back to the drain-field when the water table drops. I have been on sites where one winter the water table was -3m, the next winter it was minus 200mm. Sandy soils are worse for high water table as there is no resistance to it (although offer low vp).

At the risk of being marked as "contaminated land" in the future. You are best getting it emptied and jetted, once this is done, if there are no connections to it, fill with soil/hardcore whatever.

Get a pumped outlet, have a very shallow drainage field, it will be fine (as long as the water table is not stupidly high). Or if there is a ditch on/bordering the property, discharge to this. Septic tanks are known for not being horrendous in high water table areas and rely on gravity, so the drainage fields are often set far to low.

He is correct.

Your logic is correct, but flawed in execution. A correctly designed drainage field that matches the percolation rate of the ground (during the winter) and sized accordingly to building regs will have no issues dealing with an output from the graf style outlets (twice a day volumes).

Graf one2clean works with the control module controlling the blower and the pump, if an error code comes about it can throw the cycle off and you will have had no aeration. Once its all running again, if it doesn't go away after 5 days, just get it emptied, it won't go away. Always good to keep a spare pump and diaphragm rebuild kit for any sewage plant owners.

nothing in the tunnel, 70mm+ rocks on the bottom if you follow the spec correctly. Its basically just a huge void, water just hits the rocks and drains away, basically a hollow soak-away with an air vent.

You can use infiltration tunnels with BCO and EA approval, its very quick to get it approved. Graf make the infiltration tunnels so BCO usually state they want a Graf plant to go with it.

40m isn't that long. It will be far easier to install a package treatment plant and discharge to the ditch, If it eventually goes into the sewer fair enough. But will save you huge time and headache, and the ditch will also drain naturally for a lot of its run (i imagine).

Personally I would stick with Graf. Nothing in the tank to fail, spares readily available and top class support from Graf.