Aquafina bottle would work well too.
However, I agree with Sweetness8t5. You'll spend $3-5 in supplies (if not more) from Lowes, Home Depot, etc... and have some fugly looking thing next to your great looking aquuarium. Or spend $6-8 for a professionally looking one.
ya..... wow..... I wish my python cost me $6 ..... was more like $80 for the 50' version.