Both of them, where they go into the cyndrilical black drain trap in front of your blower fan. If you do have a drainage problem, chances are you'll get a gush of water out of one of them. The hoses won't be clogged, but the black plastic drain trap they're attached to will be.
And being a 20-year-old Carrier SX (you should really just replace that, btw), chances are it'll be clogged with a combination of brown mold and black flakes. The black flakes are the secondary Hx coating delaminating and rinsing down into the drain trap.
I dont know why people are so persistent on immediately calling a technician out instead of just giving as many suggestions as possible.
Because, malfunctioning gas-fired HVAC equipment can create danger. Like burning your house down danger or poisoning your family with carbon monoxide danger.
And judging by every post you've made in this thread, your actual qualification to do anything beyond a filter change ranks somewhere just above that of a starfish, in spite of all the 'learning a ton about something you own' that you've done. The only reason I'm posting what hose you should look at is just in the hope that you'll quite monkeying with your furnace and call a professional already. It's not a dishwasher or television set you're messing with.
Sorry to sound harsh, but I have to deal with destroy-it-yourselfers on a daily basis and you are fitting the mold to a T here.
