Possible Clues:

• A 4 down to use to clean 23 down, perhaps?
• Marine creature with a body full of pores and channels
• Kitchen spill absorber
• Cadge, freeload
• Home Counties harbours smell cleaner
• Act like a parasite
• A skeleton in the bathroom
• Very light cake
• Porous mass to be found in oceans
• Marine animal’s nasty smell — in sea, mostly