Digital BW, The Print

I have an Epson 1280 with an MIS CIS loaded with VM inks. I let the thing
sit for too long between uses, and now the black (K) jets won't print. I
did the usual unclogging tricks, with no success. Then I tried sucking
ink from the bottom of the cart with a syringe... and it feels like
something's plugged: the plunger goes right back when I let it go. Then I
pulled the feed tube off the top of the cart, and stuck a syringe on
that, pulled back; nothing, just a total vaccuum that pulls the plunger
back when I let it go. Would I be right in guessing that the tube's
plugged? Anyone else seen this?

Harry