It is supposed to remove the debris / particular such as fish waste and leftover fish food, and anything that is not gravel.
Are you saying these debris get stuck inside the siphon?
By the way, what filter are you using?
Filter media (aside the carbon pad) should be not replaced. By doing so, you remove all the beneficial bacteria for the aquarium nitrogen cycle. Basically, your aquarium will start new again after you used new filter media. I would only gently squeeze the filter media in a bucket of tank water or water treated with aquarium water conditioner for cleaning.
