Fremco 45 mm cleaning sponges, part 103-2045060, come 10 pieces to a pack for proofing conduit before a fiber optic cable blow. Driven through by compressed air, the sponge sweeps out water, silt and debris and verifies the duct path is clear, which is the cheapest insurance against a stalled cable partway down a run. Sponge diameter must be matched to duct size so it seals and sweeps rather than tumbling past the debris. A routine consumable on production blowing crews. Available from Millennium as part #587343.