This is kind of funny but it worked. I had absolutely no sponges at the house, but had leftover diapers our granddaughter outgrew. I thought outside the box and ended up being impressed with the outcome. I opened up the diapers and placed in the remaining tank water. Viola, it immediately began absorbing the water. I used 4 diapers and it did the trick. Just have a leak proof trash bag on hand. No sponge, no bucket, no mess!