The old brewmaster said:
- Know your water.
- Keep good notes.
- Clean your pipes.
Then, when the beer has departed the brewery, and is gone from the brewer's control ...
A good draught beer is only as good as a clean draught line. A chef changes the fryer oil; a car owner changes the engine oil; a bartender must clean the draught pipes (lines), and often.
Two months is too long to wait: a dirty line can easily develop an anaerobic infection. It's harmless, medically, but foul, organoleptically. Translation: it tastes terrible.
Gunk, like yeast and beer stone (calcium deposits), accumulates. Clean the pipes at least once every two weeks, if not every time you change a keg.
A series of photos demonstrating line-cleaning technique: here.