Why have a pump for the bathtub?

I could hear a faint 'splosh, splosh' and the water evacuated the boat via one of our many outlets. After only a minute or so the tone of the pump changed and Geoff waved at the switch again. 'That's it, the pipe's empty. Turn it off, can you?'

'Do we have to go through this every time we want to empty the bath?' I looked at the now silent pump. 'Why can't we just pull the plug and let it drain away? This rigmarole is going to take bloody ages.'

'Marie,' Geoff looked at me with a slight frown. 'The bottom of the bath is well below the water level. If you've found a way to make water run uphill please let me know, because we can negate all the laws of physics and make a great deal of money.'

I stuck my tongue out at him. 'Nobody likes a smart-arse, you know.' I went to put the shopping away.

Marie Browne, Narrow Margins (Mid-Glamorgan: Accent Press, 2009),  p. 154