Ink refill

Just refilled the black ink cartridge on my HP 3050 printer (it's a 301 cartridge) and it was pretty easy and seems to be working fine.
The kit was £4.50 from tesco and has 90ml of black ink, I used about 7ml to refill but it was pretty dry so maybe could have got 15ml in if I tried again.
Better than £11 for a new cartridge!