For many years I've used a Rainbow vacuum, which uses a reservoir of water as the filter. While I'm quite pleased with it, I've found that when trying to vacuum cement dust or wood ash not all of the particles are captured in the water. I believe a remedy to this would be to lower the surface tension of the water. Yes, I can always be sure to use hot water, but I'd like to go further. Obviously I can't use a suds-producing detergent because the vacuum produces lots of turbulence in the reservoir.
What commonly available chemicals could I use that would give me the greatest reduction of surface tension? So far I've tried to research trisodium phosphate, sodium carbonate, and a product called Haemo-Sol which is a non-ionic surfactant... but I can't find surface tension numbers for any of these much less the concentration to use.
The manufacturer suggests adding a tablespoon of vinegar, which I think is rather lame.
Can anyone make a good guess or point me in the right direction?