Contaminated Water

[RHightshoe@aaamissouri.com]

We just got back from vacation.  While we were gone we had a young lad
tending to the horses and mules.  He didn't notice that there was a rotten
dead bird in one of the water troughs.  I drained, scrubbed and cleaned the
tank but my mule refuses to drink from it.  Does anyone know a trick to
entice him to use the water trough a time or two until he readjusts and
realizes the water is safe?  He doesn't have any apparent hydration
problems so I believe he has been drinking from the mossy old green pond in
his pasture.  I just feel better when he drinks clean water.