Farm on plain somehow filled with rubbish (10)
I believe the answer is:
plantation
'farm' is the definition.
(thesaurus)
'plain somehow filled with rubbish' is the wordplay.
I cannot quite understand how this works, but
'rubbish' could be 'tat' (low-quality items or material) and 'tat' is found within the answer.
an anagram of 'plain' is 'plani' which is present in the remaining letters.
The remaining letters 'on' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'on' is the link.
(Other definitions for plantation that I've seen before include "land for crops" , "settlement" , "Cotton, slave, estate" , "Coffee-growing estate" , "growth area" .)