I would highly recommend that you fill through the top , another member wound up pulling the whole valve out along with the needle , I wouldn't fill a genuine 3.1 through the fill valve either , the spring in there is tiny and bound to give out , but I find that the 3.1 design has better airflow than the R91% or lite clones so it's easier to dial in for flavor IMO .Thank you thats awesome information. Also, would you happen to know why can't i use the inlet of the kayfun clone. Will it be ok if I use a needle as recommended earlier.