I am all about DIY, but all these ways seem like a lot of work to me. Why just pick up a small internal filter or a power head with a foam prefilter. Both of these can be had for less than $20 online. Also, it always seems like a shame to cut a tank when someone like might want to pick it up at a garage sale a couple years down the road
My tanks will go to a sale when my estate is settled and not before. I have donated a few to schools and nursing homes, but I still have and operate some old tanks.