This is the tool dog and others are referring to: Scissor-Style Cutter - RIDGID Professional Tools
Work it back and forth on larger size tubing. It's for black poly and soft plastic hose. If you're cutting PVC you need the ratcheting type with a sturdier blade. You can find the scissors type at most hardware stores as well as big box stores for $10-15. They're too inexpensive not to have one in your tool box and beat the hacksaw to pieces.