Wave soldering - using Pot solder
To do dip soldering you first flux the board (for example by dipping it into liquid flux). There is no rush to solder after this, you can even let the flux dry. It helps if you can preheat the board to approximately 100°C. 

The solder should be at the proper temperature before starting. Skim the dross to one side, leaving a shiny surface, then 'roll' the PCB into the solder starting at one end until it is flat in the solder, then lift the part up that was lowered first. Total time should be a few seconds. There will be much sizzling as the flux boils off. If the solder is too cool it won't clear the pins well. If it is too hot you can damage parts or the board itself.