Only just saw this, but here goes. I had a similar idea because we had all our waste water (dishwasher, washing machine, shower, fosse overspill, etc) going down a pipe neat into our field. I looked at similar things to aquacells, but couldn't find one anywhere, even online, here in France. I then looked at a 'bac degraisser' system which is great. In the end I gave up on the ones on sale anywhere within a couple of hours. We were doing a family visit to Switzerland and I'd seen their ones online and so ordered, borrowed trailer for the holiday and brought it back. All waste pipes feed to it, just in the field, I have two inspection 'manholes' that are also junctions of various pipes before, so can deal with blockages and so on easily. Out of the bac I have pipes (the 12 cm or so bore ones, flexy with holes for the water to drain out) they take the water out to a bed of fine gravel (10cm-ish), above charcoal granules (8cm), with normal pebbles below (20cm). The main out pipe feeds to 8 out pipes spaced 25cm apart and all 4m long. The pebbles are about a metre further and I have a small outlet pipe so that some water flows out anyway and I can take to sample occassionally. I have an inspection shaft so that I can check mu filtration that was planned for five years but will probably last ten. A SPANC guy had a look and said he had nothing to say because it was well above the required standard. In fact I used Swiss instructions for the soakaway system and they are several times stricter than the French.
It did not cost me an arm and a leg, I think that because I did it all myself I also got what I wanted. We have a small river just down in the bottom of the valley and I am aware of the underground springs feeding it and wanted to make sure that whatever the previous occupants had done, we did not pollute our two hectares of pristine meadow or the river. We have limestone under us, which takes in and filters a bit as well, so look at your terrain as well before deciding on what system you choose.