Raindrip makes a container drip system kit that does wonders (I had a similar situation two months ago). I used a couple of home depot hose adapters to rig a 5 gallon bucket as a reservoir and let the timer (included in the kit) and gravity take care of the rest.
you could hook up a drip system with a digital timer running a pump. if you use a small fountain pump with 1/4 tubbing leading to each plant you could have them perfectly watered while you're away and no expensive drippers or filters needed this way.