If it’s stuck down in the U bend undo it as already described:
If it’s a big cap and it’s sitting just below the plug hole you’ll need to either: poke it up from below (after undoing the u bend) or poke a hole in it from above and hook it out.
If it’s wet it’ll be very hard to make anything stick to it but if you can get a wire coat hanger and undo the twisted ends you can heat the end with a lighter and poke it straight down through the plastic cap. Then twist it so the wiggly end goes in like a corkscrew and pull the cap out.

Got a mechanical engineering education and went into a slightly different engineering field for work. Never do stress analysis.

Except this exact one that comes up every so often around the house. 😆

Another win for the shop-vac.

Looking at the age and construction of the property I guessed you must be in the UK, but that extension cord looks like you must be in the US.

For a white bowl we use a Rustoleum product called Whink and it works quite well. Don't use it if the bowl is not white as it will mess up the color.

I thought you were talking about "stained concrete" not concrete with stains. I stained my own floors with an acid stain.

Our pain is self chosen

It does and it should

https://spax.us/uploads/resources/S-1703-SPAX_Rev_5-19.pdf

I think that first sentence was crafted with care.

Please yes already

Should it have / does it need a drip groove on the bottom?

You are most welcome :)

These things seem like really daunting tasks, but are actually rather easy (more-so when looking-back, of course <smile>).

Remember that Your yard is your playground, and you can always modify what you have done, later, if your mind&perspective changes.

I came here expecting to find lots of "staring at your rear entryway" jokes and was pleased I didn't. I need to get off the internet for awhile.

That sounds like a lot of work! It's great that you could replace the threshold yourself, and the end result looks fantastic.

Right, but before we get into that, can we discuss the polyvinyl chloride?

The PVC? Because what’s up with it, also, why?

Have lots of iron in the water - even with a filter there are some stains. Best thing I found:

https://www.lysol.com/products/bathroom-cleaners/lysol-toilet-bowl-cleaner-with-lime-rust-remover

I glad you brought that up.

Ugh. Burying it is probably the "right" way to do it. Looks like asphalt or concrete though. Time to "upgrade" that to brick?

Definitely see why it wasn't initially buried. Having all that water dump into a non-porous surface (which may also not have a good grade) is bad...

It's a pretty soft steel. I think it's used more for tensile strength than for bending strength. It might work, it just looks like 1/4 inch tubing you're trying to bend back into shape.

Under the sink you should have a curve that goes down from the drain, then comes back up, then into the wall. You should be able to unscrew two places and take the “macaroni” shaped part out, and clean out the whole vertical part.

First shut the water off. This is just in case you bump the faucet levers, not strictly necessary, but a good safety net for a mess.

Second, put a shallow bowl underneath, as some water will come out.

Third, unscrews the two nuts that hold the lower curved piece in place. These parts will stay on the wall side (just slide them up and out of the way), and will come off the vertical piece. As you do this; note where the sealing rings/washers are and which direction they face.

Fourth, if your sink has a drain plug you control from above, you may need to unscrew the small control arm under the since that connects to the drain plug assembly. It’s a steel rod with a small plastic ball on it. Remove that part first, and then lift the plug out from the sink.

Fifth, at this point you should have a clear, open tube between the sink and your bowl underneath. Taking whatever you have to push and scrub to clean it out.

Sixth, put it back together in reverse order. Some Teflon tape on the drain control “arm” where it screws into the faucet would be wose

More info plz. Is it stuck in the drain ? Ie. can you see it ? Or has it gone down the drain and is stuck in the pipe ?

Thanks this is a project I will have to do (or should have done by now) and seeing this made it look much less daunting.

Leave it be, it’ll weather