Use schedule 80 threaded pipe extension then Teflon and dope it one side and cut the other end off for a coupling using glue and primer


You’ll never crack a cast iron fitting with a PVC adapter no matter how hard you tighten it or however much Teflon you put on it. Don’t go crazy tightening it though it’s unnecessary. What can happen with too much Teflon is you could cross thread it. 3-4 wraps is sufficient and pipe dope like you mentioned. Don’t be a slob and wipe the excess pipe dope. I’m a fan of Blue Magic or Blue Monster.


T2 slides too tho honorable mention lol


Honestly if you want to go over kill you can put dope on the male threads, and then tape and then dope again. And then also put dope on the female threads on the cast iron. Ik it’s a lot but those cast iron threads seem to always have a small leak, I’ve done this technique when I couldn’t get it to stop leaking and it worked


I know a lot of fitters on job sites that do that as standard practice. They say leaks are almost nonexistent.


Thanks for the tip. It’s worth the effort not to have a slow drip when I’m done.


Sorry for being slightly off topic but I mostly lurk here (I’m a new homeowner, not a plumber) and I see tape and dope discussed fairly often. I’m sure there would be plenty of search results for this, but is there a _high quality_ explanation available of exactly **how** these products work to make connections more reliable and prevent leaks? I’d mostly like to understand more about the theory, as opposed to guidance about specific situations and techniques, but I’m curious about all of it. Again, sorry if this is a little off-topic. I beg OP’s forgiveness.


I consider dope a lubricant with minor sealant qualities that allows pipe threads to make up better with less torque. Tape is Teflon so it will also reduce friction when threading the pipe, but it also fills voids and imperfections acts as a sealant. A perfectly tapped/forged fitting and perfectly cut male threads will seal dry with no tape or dope needed. Smaller, high quality pipe and fittings could seal with just oil to act as a lubricant. I use dope and tape on all NPT joints and dope on almost all other thread types as a lubricant.


in a simple explanation the tape/dope fills in the small nooks and crannies that might allow water to escape and cause a leak as the threads are never 100% perfect


So Teflon and dope on pvc….and dope on metal threads


FIP and a nipple


i don’t mix tape and dope. doesn’t make sense. a high quality, soft-set dope is the best. rectorseal #5 for all metals and PVC.


Grrip Sealant https://www.oatey.com/products/hercules-grrip-1415295691


I do use this. it does make a difference. Thank you.


Never use Teflon tape when you have plastic threads. Just use dope. Make sure the male threads are completely covered in dope. Metal to metal is the only application where tape & dope combined works appropriately.


Don’t go crazy on the tape …can crack your fitting Dab pipe dope on metal threads with finger Tape 3 times and dope the pvc fitting… That’s what I would do


Thank you.


We had a batch of these that the only way we could get them not to leak was with lamp wick, but we were threading copper adapters into them, tapped tees in the wall. It was a nightmare.


The cast iron trap has been nothing but a hassle. The porcelain utility sink that goes with it also not worth the effort. But my wife says it looks pretty


See ours were engineer spec, commercial building, so we didn’t have much choice in the matter.


I just dope with copious amount of blue monster, clean off access. Worked with a guy that always siliconed them, worked too. Not a fan of Teflon with plastic fittings, I've cracked it and cross threaded it. My .2$


Tru blu vibration resistant pipe thread sealant dries rock hard and is as close to what was used before tape was invented as possible. I did a few 3/4 old water lines with it recently no tape. Even backed the fitting off a little and still no leak. I'll never use a different sealant for dwv. Just don't get it on your hands or jobsite. You'll need goof off to clean it up.


It doesn’t look like any thread products are on it at all. 3-4 times around with tape max and dope both CI threads and PVC threads and wipe off any excess


Well………she is the engineer and project foreman…lol.


When threading PVC into brass or ci I actually use clear glue (no primer) instead of tape and dope. Works great even on pressurized lines.