I had that awful taste too when filling a new fluxo than used bad's advice disassembling washing heating up the cup carefully with a bic lighter than dry burn, than reassembling (I used one of the old clear silicone seals rather than using the o ring) burnt rubber taste gone. I think it soaks into the cup from the black rubber seal or something because even
vaping without cleaning and burning without any seals gives that awful taste on the LR versions, I didn't get so much of that taste on the higher resistance versions.