Why is there a drip after I replaced toilet innards?

Question

I replaced the innards of my toilet with something like this, all went well. The toilet works, etc. It involves undoing the water pipe, replacing insides of toilet, then screwing the water pipe back together. I had no problems, but after finishing everything up I'm still getting a small drip from the pipe (underneath toilet base, near shut off valve).

The instructions say to only tighten the plastic pieces by hand, I've done that as much as I can. But there's still dripping from the piece that connects the toilet and the pipe.

Any tips? The instructions make it clear not to tighten with tools or use sealant. It did not drip before I unscrewed it and put it back, and there was no sealant. Do I just need to tighten it more?

Edit: Here's the pipe, it's not plastic sorry. The top black piece is new and came with the parts I bought, the bottom piece is old.

Answer 1

The toilet connections shown depend on rubber gaskets to make seals. These seals likely need replacement. In addition, I see that PTFE (white colored) tape was used. It should not be used for these fittings (or any compression or flare fittings), and can cause leaks.

Disassemble the connections. The top leak is likely caused by the washer (inside the toilet tank) not being seated correctly. The gasket should have come with the replacement fill valve. The tank should be cleaned at the location where the gasket sits. I can't tell for sure, but the nut holding the valve onto the tank looks a little bit undersized. It should completely cover the hole in the tank.

The metal flare tube also needs a washer in order to mate with the fill valve. This washer should be replaced. I would tighten it hand-tight plus 1/4-1/2 turns. In addition, the nut should be cleaned of the debris visible in the photograph.

Another reason could be that the tank was cracked. Sometimes, hairline cracks are very difficult to see, but are able to produce leaks.

Answer 2

There is a good chance, especially if the existing pipe is old, that you may need to either replace the pipe with a new one and new seals. If the pipe was metal you could probably get by with just replacing the fake rubber seals in the ends but from what you've described it sounds like the connecting pipe is made of plastic.

Over time the seals in the plumbing fittings will harden as the plasticizer leaves the material. The hardened seals also take a "set" in their shape from the long term position. When you come and undo these connections and then reattach them the "set" does not perfectly fit to the plumbing fitting surfaces in its new possibly altered position. The hardened nature of the seals also means there is loss of compliance for the seal to smudge down tight on the mating surfaces to re-seal the connection.

Plastic connecting pipes can take on a malformed shape that is not optimum for the shape of the seal. Think of the pipe being slightly out of round being used in a fitting and with seals that are designed for a totally round pipe. This can lead to leaks when joints are taken apart and then re-assembled. Sometimes a new seal that is nice and compliant can be used with out of round pipes and make a good seal.

In the long run it is often the simplest to just replace the leaking pipe with a new one. I like to use the flexible type that are sheathed with the woven stainless steel mesh.