Just ordered 2Available in M6x1.00 and M6x0.75 threads and comes with a 15" tube, this one was mentioned over at SOHC4 where this is called, "the clear tube method".
https://www.ebay.com/itm/204117788121?hash=item2f865e45d9:g:rYwAAOSwq99jRb7g&var=504657473006
EBay Item Number 204117788121
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