This is a better option.

http://www.dreamworksrc.com/catalog/High-Flow-Air-Trap

You are saying 1/8" i/D in tygon. So 3.2mm bore, 4mm id / 6mm od clear is a better tube externally on the tanks.
I guess KT use 4mm od tube to the turbine from the pump, but to the pump use large bore throughout