Cleaning out a small goldfish tank

Hi there,

I've got a small goldfish tank with two goldfish. To clean it, I've been
putting the fish into a bowl of clean water, then cleaning out their tank
and gravel in the bath.

The tank is probably too small to bother with a filter, but is there any
other way to keep the water clean without changing it every week? Are there
any small water creatures I can get that will keep it cleaner for example?
I've also read somewhere about some sort of 'water hoover,' would that be
any good for what I'm talking about?

Thanks for any advice.

Regards,

Stephen