A method of thermally joining plastic eavestrough allows plastic eavestrough systems to be considered in more applications including traditional aluminum eavestrough systems where long lengths of continuous eavestroughs are desired. The method allows end to end joining of plastic eavestrough with a thermal joint therebetween or an angled connection with a thermal joint therebetween. This allows plastic eavestrough systems to be customized on site for improved performance and appearance. Thermally joined plastic eavestrough sections either aligned in an end to end or angled connection are possible.