eliminate stray +1

re-reading this, there was a +1 lingering from an older version.  I think this is finally done unless someone wants to improve it further.  Playtesting with six unchecked funnel&canteen pairs, left the area for two days. Not one bit of lag or hiccup was noticed.  Funnels mostly filled as expected.

one issue:
two of four funnels did not fill until I left the z level and returned (that inconsistent trigger).