As part of my job,I get to talk to various engineers. In a recent conversation with a Fuel system engineer. We talked about the cloths that draw oil out of water if you spill a bit of fuel or oil ,and he said you can do the opposite also, by using the absorbent part of a disposable diaper, You can put it in a sock with room for it to expand 3-4 times. and tie a string to it and let it lay on the bottom of a tank, , I tried it and it works as advertised,, Just dont let the stuff get out as it turns to a jelly.