I have a Lanbitou 3059, which I believe to be a clone of a TWSBI Eco, but I am not sure how close a copy it is.
Anyway I want to remove the piston assembly to give the thing a really good wash out as I have been using it with Diamine Registrar's Ink, which is an iron-gall formulation I believe.
Anyway, there's some ink between the two seals of the piston.
It needs a thorough clean with warm soapy water before I contemplate using anything else in the pen.
The Lanbitou 3059 really is a 'nothing' pen to me. It does have a really fine nib, which is it's saving grace. The huge ink capacity isn't that meaningful unless you have found an ink colour you like enough to buy a good sized bottle.