Found these interesting tidbits:
Do I/you need a condensate drain trap if you have a condensate pump?
Yes, you need a condensate drain trap, even if you have a condensate pump. To repeat, the purpose of the condensate drain trap is usually to stop conditioned air from being blown outside. And this same logic applies if you have a condensate pump. However, without a trap, you will blow conditioned air into the pump, usually in the crawlspace, basement, or attic.
Are condensate drain traps required?
No code requires a condensate trap. However, IRC 1401.1 (we use the IRC here in Virginia) requires following the manufacturer’s instructions for installing “heating and cooling equipment and appliances.” You will be hard-pressed to find an AC installation manual that does not require condensate drain traps. Below is a diagram from a Carrier AC installation manual as an example. Notice that it requires installing a trap on both condensate drain lines.
Checked the manual from our just installed Carrier system and it does "require" one.
Copied from here:
Your Air Conditioner Needs a Condensate Trap