I hire a petsitter who maintains tanks. About a month before I go away, she comes over and shows me how she does the wc's. I also prebag the food to remove room for error. I make sure all the supplies are clearly set out for her. i only have her water change my discus tank and my snail growout, as they are the most sensitive. The others get fed every other day and topped off if needed. I have been using the same pet sitter for 3 years now and am extremely confident in her. Also, if they are an accredited petsitter they are insured. Mine also brings in my mail, takes care of my cats, and checks my pool and vegetable garden. All for $8 a visit. I found her through:
http://www.petsitter2.com/
I checked references before hiring her and have been very pleased.