Fellow fluther chemists, and/or machinists, how would you solve this?

Work question for you. One of our gas analyzers has a clog at the bottom. Without going into too much boring detail, basically at the bottom of the combustion chamber there is a cup with a hole in it. That hole connects to an S shaped metal tube that’s about 6 inches in length, and welded to the bottom of the cup.

About the S shaped tube: We believe it is brass, coated in some kind of other metal (possibly steel but we’re honestly not sure). Its flexible, but not very, and banging it against corners of tables (for reasons I’ll explain later) will leave little “chip” marks on the outside of the tube. The tube is an S shape, but now think of it in 3 dimensions. The top curve of the S is twisted 90 degrees, so if you were looking at it on a flat plane such as an S on paper, the top curve would be twisted out towards you. At the dead center of the S there is a smaller offshoot tube in an L shape, that connects to the center of the S through the smaller line of the L.

We have a blockage in the S tube, and we believe we’ve narrowed it down to somewhere between the offshoot L-tube and the bottom of the S (or the cup at the bottom of the combustion chamber). Using a makeshift snake we were able to scrape out chunks of molten metal and carbon, but unfortunately we can get no more to come out. We’ve tried poking it continuously with wire of various sizes, using our makeshift snake (a pair of small high tension springs), banging it on the table in the area of the clog to loosen it, sonicating it in a methanol bath for 30–45 minutes, firing high pressure air through it, blasting as much high pressure water through it as we could… and we are at a loss.

We have a flow, but its nowhere near as fast as it should be. We are considering trying to dissolve the blockage but are not sure what to use. This is where the question comes in. We’re afraid to use acid (we have high purity sulfuric, nitric, chloric, fluouric, etc) because we fear we may damage the tube. Do you guys have any ideas as to what might dissolve the clog, yet not hurt our tube?

(late breaking news from our analysis of the blockage we pulled out…. the blockage was roughly 40% Sn, 20% W, 8–9% Cu, and ~20% Fe)