Just another thought related to the "longshot" advice on the previous page...
Occasionally, I get that strong, unbearable off-taste from certain tanks: to my taste buds, "grassy-metallic" provides the best description. I always thought it was either my wicks, or mysteriously hidden or super-strong manufacturing oil. But that same wick material tasted great in dozens of other tanks and drippers.
The Tilemahos and the Flash-e-Vapor V3 have been the worst and most persistent culprits. They had been wicked with reliable batches of Koh Gen Do or rayon, and tested with the same max-VG/3mg e-liquid. Before I first built them, both of these tanks had been cleaned thoroughly multiple times with soap/brushes/hot water, dishwasher, and alcohol. To no avail.
Last week, however, when I was struggling with the Flash-e, I thought about the Tilemahos and Flash and the unusual length and ID/OD of those thick-walled chimneys/drip-tips. Just a hunch, but I took a bunch of pipe cleaners and Dawn dish soap to the Flash pieces and scrubbed the .... out of them, then rinsed them for about 10 min. with very hot water. Dried, re-built, vaped: about 30% of the taste remained. So I returned to the sink & repeated the process, scrubbing harder, using a mascara brush, and rinsing longer. Taste gone. Repeated on Tilemahos and, finally, I can thoroughly enjoy that atty.
I was thinking about how filling certain tanks is difficult because the VG forms air pockets with such high surface tension that fluid flows past them. So maybe, despite all the previous cleaning, the dimensions of the tubes (and probably the composition of the steel combined w/manufacturing residue, & even some e-liquid residue) might have caused stuff to remain on the walls of those long, narrow chimneys b/c air pockets were "protecting" the inner walls of the tubes. Either that or it took the uber-grease killing properties of Dawn + a lot of muscle to finally break down whatever was hanging out in those tubes.
I'd like to test the theory using the dripper body and super-long drip-tip for the Flash-e.
Just some thoughts... good luck...I know what you're talking about and when it affects an expensive atty that vapes super-well in every other regard, it's really frustrating to have to put it back on the shelf.