While, its very good to have an initiative as for as concerns of waste products in the form of liquid poison for all forms of life. The sampling procedure depends upon the parameters you want to observe.
Depends what you want to find out. A practical way would be to take the leachate from a municipal landfill leachate collection system. There you can obtain a leachate which is from a real collected waste and had already a retention time inside the waste body.