171 sealed by a suitable closure such as an end cap 172 a first air inlet 179 and an aeration device generally denoted at 176 in the illustrated embodiment aeration device 176 is comprised of a mixing chamber in the form of a tube 177 a second air inlet 178 and a particle inlet device 180 tube 177 extends vertically to a point adjacent to the top of receptacle 170 a second air inlet 178 at the top of tube 177 permits inflow of air for mixing with the abrasive particles as described below the bottom of tube 177 communicates through an opening 174 in end cap 172 with outlet coupler 26 which in turn is connected by outlet tube 24 and tee connector 28 to particle supplied tube 30 see fig1 referring again to fig8 10 first air inlet 179 is provided in the top of receptacle 170 to vent the air space above the particle fill level 186 to the atmosphere an air filter 182 is secured over air inlet 179 e g by gluing at its periphery 184 to receptacle top 168 in use a supply container 12 is pre filled by a supplier with abrasive material leaving an air space 186 below the top 178 of mixing tube 176 as will be understood this permits air to be drawn into the tube by the suction created.