crooksey

I use Ecover everywhere, safe with the kids and no harm to my septic system or drain field. Buy the large 5LT drums online and if I am ever caught short its also in most shops.

Ross, just get the Graf and get the dosing system. You can even fit remote monitors to alert you of any failures. I have the 9PE personally and it is a great system. You can even control the discharge time, to suit. It has loads of capacity in there, for instance, I can empty two full baths, shower, washing machine etc and it leaves me loads of capacity.

Tanks come with a guarantee, if its lost its shape, its on them to prove its through no manufacturing fault. This is why building control exists, they would have had to guarantee and oversee the installation of a new tank is done correctly. I would suggest speaking to the small local builder and his building controller as a first point of call.

Agree with the above, Graf can supply a "dosing" system and you can also set "holiday mode" which reduces energy consumption. If the plant will be used in holiday mode, I strongly recommend a gravity outlet over a pumped (if possible) and adding a dual flap NRV between the water course and the pump. If you are not there in the event of extreme weather or a higher than usual water course, this will protect the plant.

As long as your proven percolation tests come back correctly, take photos and it will be fine. Only thing is, you will need to know the depth of the TP relative to the fall of the rest of the drainage runs. If you really wanted to get it in, sit the tank a bit deeper, get a pumped outlet and then put the drainage field in nice and high. Such a small job in the scheme of things, and hiring a 5t digger seems a bit of a waste when you probably have a bigger machine in when you start the build.

In theory a diaphragm should be replaced every 2-3 years. If your plant was under a service plan, this is the interval it would be changed at. I order the repair kits from ALI express and keep two in stock. £30 every 2 years isn't a huge expense.

You are over complicating this, when you dig the tank in, you will need a control box somewhere (usually hidden) for the compressor etc, so put the vent direct from the tank there.

Quite common for IC and pipes to fill with crud during the build phase, avoidable but common. Usually always cleaned out, they have used concrete risers and caps, so imagine pipes been installed with a laser level. Jetting and vac out of drains isn't as expensive as you would think.

You only need to replace a septic tank if you discharge to a watercourse (or anything other than a drainage filed). Trouble is many solicitors scare buyers as they (and the buyers) aren't really too clued up on non-mains drainage. You can still install new septic tanks today. If you are selling, I would recommend saying to your solicitor you will get the tank emptied and jetted before the sale completes and provide evidence. If its been in and working since 1983, you have no issues (unless you discharge to a watercourse etc). Also I would state how often tank is emptied and provide evidence of it, compared to waste water costs these days, its actually cheaper to have a tank/treatment plant on a monthly basis than it is to have a mains connection.

Isn't this just a normally/open closed solenoid coil?

because if you add the NRV in that manhole in the house, it would only work up to the "back" edge of the inspection chamber, water that entered the mahole next to the road would still back fill into the IC in your kitchen. If you fitted the NRV i posted into the IC in the kitchen it would be the wrong way round, and effectively block that IC from passing effluent into the manhole in the road. If you are not confident doing it, I am sure a local drainage company would be able to assist. It cold also be that the manhole in the driveway needs replacing with an "air tight" one, this will ensure no flood water enters it. It may be worth getting a CCTV survey just to check there is nothing un-toward. I see you are in Surrey, I am not affiliated with them, but I use "Totally Blocked" for all my CCTV surveys and any patch repairs that need doing. https://www.totallyblockeddrains.co.uk/.

It won't work on the IC in the kitchen, probably flows from there to the one on the drive (easy to test). It would need to be on the last IC before the property, so it does't allow backflow.

In theory, there should be no reason why effluent or water comes back through a manhole cover, unless the downstream runs are blocked. To answer your question, manhole grease should help yes. But I can assure you, if water is getting up through a manhole cover, then more foul air than you realise is as well. Something like this on your last manhole before the road could help: https://pipetek.co.uk/products/retrofit-non-return-valve?variant=31966322917494 This below video shows how NRV's can protect in storm surges:

Adding a non return valve on your drainage run before it joins the surface water (if combined sewer) will stop storm surges causing a problem on your foul runs. You need to clean and maintain them regularly.

Just so you know (in England) this is still technically legal. As long as its not discharging to a watercourse, do not let people in this industry scare you. I have seen tanks from 100 years ago still in use, someone cleaned it out, re-pointed it and added an air blower on a timer. If it was me, I would negotiate the price to reflect this. But in reality, you could move in, have the pipe from the house jetted and re-lined, jet the tank and probably be fine until you get round to installing the new system. With a healthy dose of muck munchers once a month.