Volkswagen Repair: p0441 - 2001.5 Passat V6, sedan, 2WD, 96K miles, proper nomenclature, purge valve

Question
Every time i fill up my gas tank, when the gas level drops to about 3/4 - 2/3 of the tank I get CEL with p0441 code on it. If I do nothing, just keep driving (10 miles to work everyday) the CEL will turn itself off once the gas level is getting close to minimum.
What could be causing it? The purge valve seems to be working (it's "clicking" once the car warms up). Do you think lines from the gas tank get clogged at certain gas level?
I recently replaced vacuum lines around throttle body ("just in case") but the code came back after filling the tank up and driving it for 2 days (again, at around 2/3 of gas in tank).
Any ideas?
Thanks BIG TIME!!

Answer
Hi Sobek;
Might be the "leak detection pump" itself.  If it's getting weak, it won't be able to fill the tank to desired pressure in time, and the computer will sense a leak, rather than just a slow pump.  "CEL" I understand is check engine light, but the proper nomenclature is "MIL" malfunction indicator light.  Good luck, Sobek.