How to fliter my tank?

how to fliter a tank without buying a fliter im 16 and my mom just let me get a betta after begging for 2years ( it was nothing gettting a dog compared to this we had 9 dogs at one time becuase we use ot breed them). She said they would stink sooo thats y well I just got one and my crown tail betta keeps his bowl spotless but my 2 minnows keep their bowl cloudy if I skip 2 days of cleaning it you can't see threw it well I asked my mom for a fliter she said no fliter then I asked if I could egt a bigger bowl or even a tank for them becuase my betta is in a 1 gallon and they are in the little bowl the betta came in one is 1/4'' on is 1'' they are very nasty....my betta has no stink even when the water starts gettting cloudy after a week they get dirty and stinky the night after i change the water....I like my minnows but they are gross ,and they are my nephews fish and he only comes over 4 days out of a month so they are my responisiblity to keep alive so please help me with this how do I fliter the tank without a filiter is my main question.