as longa s you have a good filter an you keep an eye out for any odd smell you can do a partal weekly. i know someone who does theirs in a 10 every 2 weeks an only takes out roughly 5 gal.
I dun keep my 10 filled up so theres roughly 5 1/2 to 6 gal in my tank since i keep fish in an have 2 eels in the same tak with mine it would become prety obious if theres a problem with it lol.
some people use test kits, i noticed alota people on here do.
al in all its your judgement call on what you want to do.
Walmart an alota diffrent petstores sell the python hoses, an syphon hoses. theres one that you can attach to your faucet, an place in your tank an has a valve on it, one for syphoning water, the others for adding water, you can also just get a cheapy syphon hose an use a bucket abn move the hose around your tank if you have anty gravel or anythinin it the syphon often stirs the gravel up an allows you to get hidden waste

.
If your not sure about one of horses go to your local petstore an ask someone on hand, you should even be able to ask them if they could demonstrate one for you. Any decent store will

an will always be happyt o demonstrate a product or even use their own products in store.
When you're a deadite skeleton, life isn't filled with a lot of options. So they make the best of it by playing dead – Which is why we like to introduce them to Mr. Shotgun, who doesn't give them the opportunity to pretend there anything but Chalk.