Waste Disposal. 
On construction site the disposal of building waste including paint and hazardous liquids should be cover at your site induction toolbox talk.
At this time information and disposal stations facilities should be available.
On domestic projects checks should be made with the local authorities regarding facilities and regulations for commercial wastage.
Under no circumstances should paint products be disposed of into the nation water drainage system.
Part used paint containers should be filled with either sand or sawdust to consolidate the liquid and allow to dry be for disposal.
Dirty solvent (white spirit etc.) is classified as hazardous and should labelled according as this type of product can be reclaimed.
Tips:
Part tins of water based paints are available they could be offered to a local community organisation.
Dirty solvents. After washing out brushes the solvent can be reclaimed for future use by transferring into a larger container. Once the solids have settled to the bottom the solvent can be syphoned off and reused.