OK, here are pics of the pump I was talking about
: continuously rated, this Johnson pump runs on 12V (just plug into your PSU), 2.2A, 26W; pumps 356 GPH / 22.5 l/min at 3ft. head.
Dimensions are 18cm long by 5.5 cm width.
The only problem is the price... $179,-- i.e. £130,--. Ouch! Regardless, I decided this will be the one for my project.
Pics below:
Whaddaya think?