...and guys knocking on doors asking if you would like to change your energy supplier so they can sell you "their" electricity, which they don't produce.????
^ The stainless tank needs a layer of trapped air to function. Drain the water from the tank by removing the unconnected plastic plug then replace the plug and...
It is quite common practice to fit stones similar to below and use the strimmer engine to turn the stones while holding the blade.
In this case he used the wrong kind of attachment (cutting disk). The rpm limit is probably OK but they don't take much sideways force.