If a hot tube blower will work in the amount of water they work in, It should more than provide enough CFM to agitate the small amount of sap that will be in the WRU. Also they must come in differant sizes for CFM. As far as air goes, It should be filtered know matter what type of blower you decide on. When you start looking at factory stuff the dollars start adding up fast! Most places that work on spa's have salvage blowers hanging around!! My repair man said he has a box of them Jim L.