I use a jug (especially for my tanks needs), and scoop out about 10% water every three days (or so.. depending really), adding new fresh water! (using a anti-chlorine chemical)
I suggest getting a 'gravel cleaner' at your LFS, and using that to clean your gravel and the poop/other gunk that gets into your tank, i recently purchased one for £3.75! LOL - It was a small one, mind you, i only have an 8GAL
Go and get one of those and clean out your every couple of weeks with it... and change your water every couple of days,
do you have a filter running?