The filter you have is not intended to remove waste from the aquarium. It simply breaks down ammonia and nitrites and produces non-toxic Nitrate. The purpose is to create an environment the fish can live in, with regular aquarium care on your part.
The water changes you do are to reduce the Nitrate buildup and maintain the buffer system, so that pH changes do not occur.
This is an oversimplification, but i don't want to make this complicated. I would continue to change water, but do so every week. Pick a small portion of the gravel bed to syphon each week, so that you are not draining to much water.
By the way, if you are getting the amount of waste you say you are, then there are only 2 options. 1 - you are overfeeding. 2 - your fish selections are poor from the size aquarium you have.
Please tell me you don't have goldfish.
What fish do you currently have in this system?