In my bathroom, the J-pipe under the sink has corroded to a point where water just flows straight out the bottom. How difficult is this to replace? Do I have to use a metal pipe (which is what is there now) or can I use a PVC part?
It isn’t complicated, but it could be a pain in the ass anyway depending on the amount of corrosion. You should be able to remove it with a pipe wrench and some elbow grease, perhaps some WD-40 if it won’t budge.
Metal parts aren’t much more expensive than PVC; you’re still only out a couple of bucks. Threaded PVC is intermixable with metal, but not the glued-up type. If what’s there is so old it corroded through, though, the ancient threads might not be compatible with new hardware either way. If so, you can just saw it off and clamp on a replacement. The friendly clerk at your hardware store will be glad to show you what to do.
Those j-pipes are usually just a fat rubber washer compressed around the smaller pipe. If you can’t undo it by hand, a pair of arc joint pliers (Channellocks) or a big adjustable wrench will take care of it. Take the old pipe to the store, and buy a new one. It’s easy. WARNING: When you’ve taken the pipe off, and dumped the gacky water into the pan under the sink, don’t dump the pan into the sink. It’s embarrassing.
You know, I’m really tired, and I thought you were hiding under a sink replacing a bong. Whew. Bed time.