I hope you not feel i am taking over your tread CuriousAmerican but i am also going into dirt tanks (my first )
This is important to both of us.
I have done a lot of reading on the internet, also Diana Walstad's great book.
Most of the litterature regarding dirt tanks recomend a cap size of 3 mm over the soil, about 1 inch thick i tink.
Any opinions on the cap size would be appriciated, also by the tread starter i think.