I took out my bathtub to replace a rotted wall behind it, and the drain pipe fell out. (Yes, I unscrewed the drain fitting before removing the tub.) The joint under the concrete slab, where the drain pipe meets the P-trap, is what came apart.
The P-trap is below the concrete slab, and not right under the tub drain, so it was extended up to the tub drain with two 45-degree elbows. The P-trap is cast iron, and so are the two 45-degree elbows. The pipe nipples joining them are galvanized steel, US 1-1/2 inch NPT.
The P-trap, however, is not threaded, at least not with 1-1/2 NPT threads. It looks like there could be a smaller, finer thread; it might be tub drain fitting threads. Or it might just be my imagination; it is hard to tell with the rust.
It appears that the steel pipe nipple was set into the P-trap and sealed with lead. The lead made sort of a gasket, sitting in a lip or shoulder of the P-trap. The lead ring was peeled up slightly on the left side. I imagine it may have had a small gap with a the P-trap for a long time. I attempted to peel it off with pliers, as you can see, but it is held quite firmly on the right-hand side.
This type of connection is used elsewhere in the house. Here is another one nearby, which I think is for a vent stack.
The house was built in 1966, and I assume this is original construction.
I scraped the joints with a knife, and I'm quite certain they are lead. There is no clearance gap between the galvanized drain pipe and the cast-iron P-trap hub. There is no oakum; this is not a bell-and-spigot leaded oakum joint.
So: what's the best way to repair this pipe joint? I have replaced the bottom pipe nipple on the drain pipe with a new one, but how should I reconnect it to the P-trap?
I'm sure I can clean off the old P-trap and set the drain pipe back in place (after I measure and position it carefully to line back up with the tub). How should I reconnect it? I can imagine several alternatives:
- Re-melt the lead by heating the cast iron P-trap with a MAPP or acetylene torch
- Remove excess lead and pack with epoxy putty
- Dig out the P-trap and replace with a threaded one, perhaps in a better location.
I really don't want to replace the P-trap buried under the slab if I can avoid it. I'm leaning towards trying to remelt the lead, but I don't know what pitfalls to avoid.
Advice? Suggestions? Thanks in advance for any help.