non polar solvent. easiest way to clean glass pipes and metal pipes is acetone soak. now I know this sounds poisonous but, if you are careful and use the substance as a soak no wood pipes or organic based pipes. after you soak them for a bit then boil them in water as to extract anything left behind it should be safe. from my personal research, ive found that acetone itself will leave no residue after air evaporation. however when included in other substances it can bind. espesialy with organic materiel. that's why I say glass and metal and then a water boil.
here is how I do mine. clogged pipe goes into a sealed quart container safe to be filled with acetone. like a coffee can. then let sit for 2 days. extract the pipe with chemical gloves or tonges. then let sit to evaporate. if theres any substance still on the pipe I empty the container and clean it. refill add the extra tone and re submerge it. most of the time you will not need to do a second soak. then after your pipe has completely dried and has nothing I it. I boil it for a half hour just to be sure. if you keep your goo in the acetone you can actually let it sit awhile completely dry and smoke the resin extract. as long as its only cannabis. like I said acetone bonds with polor organics. cannabis is a very weird plant because it non polor as is the acetone solvent. also get as pure acetone as possible no addatives as ive found the cheapies to leave residue.