I did mine by hand and gave it a slight 'nip' with a 30cm ratchet. 25Nm isn't much above hand tight. Whoever had previously done mine had done it up so tight I needed a 60cm 'breaker bar' attachment on the socket to undo it. With it being plastic that meant undoing it VERY carefully in case it split. And with there being an 'O' ring seal in the cover it doesn't need to be that tight - not like older cars where the ring around the top of the seal needed to be properly compressed to work.
Why it had been done up that tight I have no idea! The rating is embossed in the cap after all.