John Gill Commentary Numbers 18:30

"Therefore thou shalt say unto them, When ye heave the best thereof from it, then it shall be reckoned unto the Levites as the increase of the threshing-floor, and as the increase of the wine-press." — Numbers 18:30 (ASV)

Therefore you shall say to them
The Targum of Jonathan is, ``you shall say to them the priests;'' but the words seem manifestly spoken to the Levites:

when you have heaved the best thereof from it ;
taken out the tenth part of it, and that the best:

then it shall be counted unto the Levites as the increase of the
threshing floor, and as the increase of the wine press ;
then what remains shall be reckoned as much their own, and may be as lawfully enjoyed, as the corn of the threshing floor, and the wine of the wine fat, of any Israelite whatever.