Yes this all does seem a minefield. We are currently gathering the materials to install our fosse and filter and unless you buy an installation kit, ( wait about 4 weeks) the builders yards seem very ignorant of some of the materials being asked for .ie. geogrille as opposed to textile etc. Has anyone else found this? Or am I just missing the fact that geotextile and geogrille are the same. On the matter of cost, we were quoted 6500 euros for a system 18 months ago, with a pump out of the sandfilter, but have had to resort to guided diy because of costs. I expect this has increased even more now.