Air Conditioning - unclogging [A/C] drain line

We are going to unclog the drain line off our furnace/ac which is causing a leak and water all over the floor. Before we start i had some questions. There is not an easy access point so we will have to cut it and then mend it (its cpvc). It goes about 20 feet across the basement into the sewer lines through cement, so cleaning it out at the end isn't an option. i was going to cut the line right after it comes out of the furnace duct tape ( to create a seal) the shop vac to the drain line ( not the part going into the furnace) and suck all the gunk out. I think our shop vac only sucks, and cannot be reversed. Is this ok, or do we need to blow it out into the sewer? Also i noticed the drain line is also connected further down into the furnace off a T near all the parts and there is a clear little hose coming from the furnace into the line, then it hooks into the drain line from further up, the clear piping looks really dirty inside (its all green) although I know this is not where the leak is coming from, is this a problem, and will I harm the furnace if I would suck out that line? Any other tips for doing this would be greatly appreciated, thank you

The drain should not be going into the sewer. Now that is said, I would suggest blowing out the line to the sewer & sucking out the part going to the furnace. If there is someway you could hook a garden hose to the part going to the sewer, that would be a good way to blow & flush out that part of the line.

after talikng to a guy at work, I know why my drain line is clogged and i understand why it shouldn't go into the sewer. Last fall there was major flooding in our area, and although we didn't flood we did have sewage backing up ( I guess it has to go somewhere). Since we never have any flooding problems ourselves we capped the floor drains in the basement to keep this from happening again. When the sewage backed up it must have gotten into that drain line. Since it was fall we didn't use it until this summer and now we have the problem. I will be removing it from the sewage line and giving it a proper home. Oh the headaches of home ownership! You have been so helpful, I appreciate you giving up your time to give out advice.

All of us here enjoy what we do & have been in the same kinds of situation as you. I suggest you install a union where you put the drain back together. This will make future routine maintenance easier. Make sure you seal where the drain goes into the sewer. You don't want sewer gases or sewage coming out of there.