quote:

Originally posted by vulrath:
Thick, opaque white sludge.

Grey = grease. Black = soap. We never "learned" of opaque white, but I've seen it in beer cooler condensate lines. I'll stick a hose in the top, above an open tee, and flush the potential blockage into a sump.

Does it feel slippery, not soapy?

Can you see where the condensate line ties into the drain (a branch off a branch)? Or is it inside the wall but you know it is there?

Plunging never clears? That would possibly mean the blockage is after the condensate line connection, and the plunge force is going up the condensate drain.

Is the condensate line connected to the pan or to the fan coil? Is the pan all full of crud?

The pipe within the wall/floor could be back pitched. The condensate line has nothing to do with the issue. Soap is collecting in the belly of the dip.

_{If the stack is close you can open the adjacent wall and put a saddle tee on it. Not code, but it will solve the problem.}

Out here in the sticks we have a septic tank system, so dumping bleach and such is out of the question. I've had problems too, and found that using Ridex in my sink drains (kitchen and bath) makes for a much happier running drain. I'll treat and add a cup or two of hot water to get the stuff down the pipe, then leave the house for a few hours. Once home again I heat water on the stove to near boiling and dump that down drains again.
I still disassemble the elbow trap every year or so and snake it, usually a couple of days after treatment. I'd rather deal with it without a clogged drain and a sink full of nasty than try to bail and make an even bigger mess.

Google "Thrift drain cleaner". My plumber introduced me to this product. It works great.