[chopsueyar]

I've used inexpensive bilge pumps from Walmart or Sears and a 12V relay.

http://www.walmart.com/ip/Shoreline-Bilge-Pump/16609596 These start at $13 for 600 GPH.

Then use a 5V relay to switch the 12V relay.

http://www.radioshack.com/product/index.jsp?productId=206248...

http://www.radioshack.com/product/index.jsp?productId=124667...

YMMV.