Replaced a tap recently (iron pipe and stainless steel tap) but it still leaks and I think I need to use some pipe thread sealant (aka pipe dope) vs the usual ptfe plumbers tape. Does anyone know which one to use? There seems to be so many loctite models, which is the one other than loctite 55 which is suitable for water pipes?

PTFE Tape will do.

No it doesn't in my case which is a metal pipe (not plastic) which is old and the tape gets too cut up on the corroded threads. Normally thread sealant is used for metal pipes anyway.

It doesnt matter is plastic or metal ... just roll as thick possible .

Using any sealant will make replacement difficult the next round.

Use the white colour tape..
Both metal & plastic...

Good only...
Got tactics to use... If Don't know.. ask someone who knows....

Yes actually I find the Taico yellow tape from CSM is pretty good.
Also available online - https://shopee.com.my/12mm-x-0.09mm-x-8m-SE...1900.2727553247

The tape is compressible so need to wind many many layers (in the beginning need to press it down abit so it goes into the threads) after that just continue winding until the other fitting cannot go in.
There is a trick w.r.t. the direction of tape and the direction of assembly.

Appreciate the replies but I already know how to use plumbers tape and know how to wrap it in the right direction.

It could work but in my case its better to use pipe thread sealant because there is a risk of breaking the pipe which has happened before.

No pipe thread sealant will not make replacement difficult, its does not harden when it is fully cured. Its the reverse actually since I wouldn't have to use as much force as I would with normal ptfe tape.