This is a design for to simplify washing ores before you have an Ore Washing Machine. It utilizes very few components:
10 Redstone Dust
4 Redstone Torches
2 Redstone Repeaters
1 Redstone Comparator
You will also need some basic building blocks, a bucket, and a water source.
Below is an walk-through of how it works, you can feel free to skip it and just follow the photos. Here's an album link, or see attachments: http://imgur.com/gallery/m4Msz
The way this is set up, when water is placed into the Cauldron the Comparator will pull out a redstone signal, feeding it into the first Repeater (without the repeater the signal won't reach anything).
From the Repeater it splits, one line heading down to feed directly into two blocks, and the other into the 2nd Repeater to create the a loop so it cannot get stuck in the off position. (Pleas note: this can become stuck in the on position, which you can fix by breaking and replacing the cauldron)
On the other side of the blocks are Redstone Torches, this creates a small delay, and feeds the signal back up to the Dispensers. I utilized this method to stop the redstone signal that feeds the Dispensers from feeding the Repeater loop as well.
This design is not 100% perfect, it sometimes misfires and you will get unwashed ore back. This is why I added the Redstone Loop in, it will continue firing until the Cauldron is empty.
Hope you enjoy,