Butt Pump
[Sniggers like another child]
To be honest it’s your best option but it will empty you butt out quickly [snigger again] or just get a dirt worker if you can get a car’s working fag lighter socket to the area.
If you are looking at a pond pump like RobS says you need to remember it needs to lift water to a height of 10meters just to get 1 bar of pressure.
A £250 Ubbink Cascademax lifts up to 6m = 0.6bar which is not enough for a normal spray gun yet it moves 18,000lph when not lifting any height.