I'm cleaning my 10 gallon and have found that the pump I had stop the uplift tube for my undergravel filter has died. I have to wait for payday to get a new one. I don't want to take the tube out and have to just rearrange the tank in a week to put it back. But I don't want anyone to swim down it and get stuck. (Yes, I've had this happen.) I've a terrible headache so I can't really think straight right now but I need a quirky fit cap for the tube that doesn't float. A cap to a medicine bottle works great but floats right off. I can't think of anything else but y'all usually have great ideas so here I am. Any ideas?