Ehehe...my perverted mind immediately went to 'sex' but of course it wasn't that since you already posted disclaimers saying that sex wasn't the answer.
I'm going to have to agree with eno1; is the answer a sponge?
Rather good riddle, you had me sitting here for a few minutes trying to poke my lazy brain into thinking (though, I must admit that half of that time was spent giggling at how easily sex comes to mind). I hope you post more of these!