What does the cryptic crossword clue "If you refill petrol, ends thus? (4)" mean?

The definition is "thus?". The wordplay uses acrostic. last letters of "If you refill petrol," = FULL; definition: "thus?" The answer is FULL.

If you refill petrol, ends thus? (4)

Guardian Cryptic #27146 | 22 Across | 2017-03-16 flower