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So it looks like the pothole I hit on Sunday has dented my rim. Interestingly there are two dents, so maybe the other one was caused by the other pothole I hit in December, which might explain why it kept loosing air.

I've read some old posts on here and it would appear that people use all sorts to undent their rims. I don't have a vice, but I do have some spanners and a hammer. Just wondering if anyone has a link to video, or some such, that shows the correct application of tools to the rim to get rid of the dents...?
I use a pair of knipex channel locks, they don't chew the rim up like a pair of molegrips or pipe wrench pliers do.
I used a adjustable spanner to pull out a dinged rim - however that one looks like it might also be out of round in which case it will not work. worth a try tho
As above, just get an adjustable spanner on it (be careful though, you might need a metric or imperial one) and gently pull it out.
I'd be surprised if a little ding like that was causing air loss though
(be careful though, you might need a metric or imperial one)
If the OP is left handed then he might need a left handed one too.
Anyway...
I've pulled dings out with an adjustable spanner before, just go slowly, you can tape the jaws of the spanner if you are really worried about marking the rim.
A disk rotor truing tool is another option if you have one.
Knipex pliers wrench and something flat, metal, and solid that gives a straight edge.
Flat edge against the rim on the outer edge, then use the Knipex to push the rim out towards the flat edge to straighten it. Using mole grips to bend the rim risks cracking it as you’re twisting the rim as you pull it, instead of pushing it.
Go slowly too.
I heard a mechanic say keep an old rim or an undamaged section of it, cable tie or tape to damaged rim and use some g-clamps to bring the dented rim back against the straight rim, I haven't tried it myself but it sounds like it'll work.
Really the best way to address that, imo, is a vice.
When that happens to me, I press that section on a big(ish) vice. This is usually enough for the rim to hold air