If h&-bailing is impractical, then water your plants directly from your rain barrel with this handy electric pump from Einhell (it can also drain cisterns & similar tanks containing clean water). It's powered by a durable 400w motor that drives a pump which will shift a substantial 4200-litres-per-hour; & it features a variable float-switch that you can fix at the height you wish the pump to start-up. The German-designed Einhell BG-SP 400 RB is of robust construction & comes with a ten-metre hose.