Well can i just say i know what u mean about waste (crap) build up, i have a 50g tank with guppys, tetras (neons & penguin), and garamies. But the worst culprits are my pleco and 3 clown fish that since they have grown up from babys have created more and more waste. I do the fortnightly water changes but i also clean it with a gravel cleaner every 4 days just to keep on top of the waste, for about 10min and empty about a buckett full. there is nothing worse than an untidy tank one of my pet hates lol

but if this is too much of a chore to do i would get an apple snail because they eat dead fish remains and there great for eating up waste so i hear but there is a draw back beacause they love eating plants too! So if you have live plants then i would say its a no no. hope this helps m8