Dialyzer is a static analysis tool that identifies software discrepancies such as definite type errors, code which has become dead or unreachable due to some programming error, unnecessary tests, etc. in single Erlang modules, applications or whole systems. Even though it is one of the oldest tools available to Erlang developers, it lacks a proper user manual since its release, due to the self-explanatory nature of its warnings. This talk presents a small practical guide to the tool, assembled while introducing the systematic use of Dialyzer in a legacy project. It deals with initial difficulties (how to run Dialyzer, overcome initial crashes, deal with the causes of common warnings and discern the important or simple-to-fix discrepancies from the rest), as well as the integration of the tool into the testing, documentation and maintenance procedures of a project (how to ensure that the code is in compliance with accurate type specifications, remains free of common discrepancies and respects the interface of opaque data structures).