Daf

Well, either the tank has established itself or the Muck Munchers I put in, a week last Monday, has worked. There have been wafts of stinky air about the place (especially near the tanks) for several weeks. At the moment there is no smell of anything in the air at all - even when I'm up close to the tank and the manholes. I think that anyone who is putting in a new tank should think about starting it off with a year's supply of these. Admittedly, I thought this was going to be some snake oil stuff but it seems to be working. If anything changes I'll report back.

I never had a problem with smell from my previous onion tank. That was a loose lid sitting on top of a breeze block chamber. Nowhere near air tight. I assumed that all smells were vented through the soil pipe stack attached to the house, at the end of a 30m run?! I think you are right about having to wait for it to establish itself. I never fully emptied the old tank and always left at least a foot of sludge at the bottom. No rainwater goes into the tank but it was filled with clean water during installation so that the pea gravel that surrounds it, could be distributed evenly and tamped down. So, the idea that the tank currently has too much water in it, err, holds water!

Thanks for the info. I've bought it, to see if it is a quick fix before the tank establishes itself. Bleach is a septic tank killer but you can use it in small quantities. It seems that since 2017 (EU legislation) most washing powders and dishwasher tablets are now phosphate and bleach free, so should not be harmful to any tank.

I have replaced an old onion septic tank and a drainfield that was no more than a hole with builders rubble (done before I owned the house) with Graf Carat 3750L and a drain field that in total is around 56m long and 0.9m wide. The system has been up and running for around a month and seems to be working well. However, I am getting some strong whiffs of foul gasses coming from the tank manhole and other manholes in the system. I know that I can buy a sealed manhole cover or use some manhole grease to seal the drains but that is a work around and probably not the cure. The soil stack vent attached to the house must be a total of 30m away from the septic tank, given the soil pipe run. I could improve that a bit by adding a rotary cowl to encourage venting at that level but it was OK with the previous onion tank. I am wondering whether I need to wait for the tank to settle down or whether I need to commission it somehow? I'm not chucking a dead cat down there, not sure about these wonder chemicals for sale on dodgy websites and unsure as to chucking bicarbonate of soda down the toilet would help. Has anyone experience something similar?

I know that the drain from the kitchen is around 15cm below the surface but runs into an inspection chamber that is 82cm below ground. I'm assuming/hoping that the bathroom connection and downstairs toilet are the same. A bit of digging will confirm this and if they are the same then I can can redesign the pipework that will work with a low level bullet septic tank at minimum depth. Still don't get the support for Sewage treatment plant over a septic tank. I have nothing against sewage treatment plants but for this installation I can't see the point?

Why do I need a sewage treatment plant? I cannot discharge to a water course and have to discharge to a drainage field. A septic tank is half the price of a sewage treatment plant, has no moving parts, no need for an electrical connection, is bigger and therefore has a capacity that is more tolerant of cleaning chemicals. The existing onion tank and drain field has behaved perfectly for 22 years until the baffle broke. Why change?

I have an onion shaped septic tank that's well over 22 years old and the baffle that separates the lower chamber from the top chamber has come loose and is now flopping about within the tank. I think some clumps of fat have now worked their way down the soakaway/drainage field and things have become sluggish with waste water throughput. I didn't install the tank or drainage field so have no idea what it looks like underground. I'm thinking of installing a new bullet shaped septic tank and drainage field as what I've read on the interweb, the existing tank isn't repairable. I can decommission the old tank, drain it, knock some holes in it, chuck in some rubble and cap it off etc so not too worried about that and I have the space to put in a new tank and drainage field in parallel before switching over. All good. (1) I'm looking at the Graf Carat 3750l tank. Does anyone have experience of this tank? Should I also look at Marsh's or Klargster offering? Any others I should consider? (2) The inlet for the new Graf tank seems to be around 600mm below ground. I have an inspection chamber outside my property that collects three waste feeds from around the house. When the house was built this drain was connected to the mains but the effluent had to be pumped up hill to the nearest mains pipe. After several failures and leaks, the original owner disconnected from the mains, removed the pump and switched to a septic tank. I think this is the reason why the pipe running to the existing tank starts at 82cm below ground at the inspection chamber and terminates at 1.5m at the onion septic tank. That is very low and defeats the purpose of using a low profile tank. So, I suspect the whole lot has to come up by quite a bit by the looks of it and I'll have to dig down to find the original pipe height as it leaves the house - hoping that it is much higher I suspect! If it doesn't where do I go from here? Another Onion style tank?