Once the pasta is done, use pasta water plus lemon juice and fish sauce and butter to finish and emulsify the sauce. Add herbs of choice and some cheese before serving.
I rarely use a colander to drain pasta. It is much safer and easier on your wrists to move the pasta from the pot to your pan of sauce using a skimmer or tongs.
When your sauce is emulsified, it will be silky and thick, lightly coating each strand of pasta with lemony, garlicky goodness. There's a reason this dish is a classic!