Apo-dhatu is not experienced through the body door , however it can be known through the mind-door.
So while the other great elements are experienced through both the body door and mind door apo is only known through one door. This does not mean it is entirely inferential or “outside of the all”.
It is wonderful how precise the ancients were in showing such fineness of classification- all of which can be known.
https://groups.io/g/dsg/message/32307
From Nina van Gorkom:> N: Only three elements are tangible object. Even as one does not touch
visible object, in the same way one does not touch fluidity or the element
of water. Someone who believes that he can touch water is only thinking of a
concept. We should verify this in touching water without thinking about it.
At the end of this Tiika text (English below):
Sesanti yathaavutta.m ruupaadisattavidha.m ruupa.m .thapetvaa avasi.t.tha.m
ekaviisatividha.m ruupa.m.
As is said, he declares visible object and so on as sevenfold *, and the
remaining materiality are twentyone kinds of materiality.Vi~n~naa.nassevaati manovi~n~naa.nasseva.
As to the expression, (they are the objective field ) of consciousness only,
this means, only of mind-consciousness **.Avadhaara.nena ruupaayatanaadiinampi manovi~n~naa.navi~n~neyyatte
niyamaabhaavato na vi~n~naataruupataati sa"nkaraabhaava.m dasseti.
By stressing this, although colour etc. are to be known by
mind-consciousness too, he keeps the rupas that are not experienced
exclusively through the mind-door separate (not mixing them with the
others).
–
This is a useful recording of some points where people wonder about similar matters:
half way through: SUJIN BORIHARNWANAKET: The teachings are not to read and doubt;
but to read and understand.
Otherwise always doubt: ‘why this and why that’