I received as a gift, a vacuum cleaner of an unknown company, that can also wash the floor. The instructions say "when filling the water-tank, use only a detergent without foam, as foam may harm the engine". I went to supermarkets, but no-one know what detergent does not generate foam.
I believe this requirement is not unique to this particular machine. My question is: what kind of detergents of fragrants can I put into it, so that they will not "generate foam" and not harm the engine? It could also be natural materials.
EDIT: I am not looking for recommendations of a specific commercial product. I am looking for more general guidance. For example: are there natural substances that can be used? Maybe sodium bicarbonate?