Ghetto tubeless attempt going alright here:
Bmx innertube cut (schwalbe 20 x 1.5-2.5 Schrader)
tyre onto the rim fine (2.1 crossmark folding with exo protection on a well used xm719)
valve core taken out fine
used the pop bottle compressor idea – works AMAZINGLY. brilliant stuff.
Had tyre up at 60psi sealed as well as you can with no sealant.

problem comes with the whole idea of putting the valve core back in and trying to use the pop bottle compressor to fill ‘er up. I want to make sure it’ll go up before I stick the sealant in.
Topeak joe blow floor pump not doing enough on its own and the cheapo compressor just doesn’t push the valve in so no air actually gets into the tyre.

What other options do I have apart from borrowing a proper compressor that’ll inject air steadily rather than the instant 60psi of the pop bottle?

If you’ve got it to inflate to 60psi and slowly deflated it the tyre should stay seated, enough to inflate the tyre normally.

If not there’s no harm in doing the bottle trick with no valve core and sealant in the tyre. What I do pump tyre up to 60psi without core, swiftly remove pump finger over end of valve and quickly insert the core to prevent any further air leakage then re-pump to desired psi.

If this post makes any sense at all!

I seat it with sealant in but no valve core, then stick finger over hole and shove the core in. It’s quite easy to do and the sealant doesn’t go everywhere ( valve at 9 o’clock tho).

Yeah half the problem is its not staying seated after the first inflation. Left it at 60 psi for 5 or so minutes but no real luck. Wondering if the bmx tube is too thick?
And surely if you inflate it with no valve core and sealant, when you remove the pump the air escapes too quickly? Has been in my experience so far!
Latest attempt, bottle up to 80 psi to try and open the valve but the tube just flew off the valve instead!
Mildly frustrating.

Ah ok, two saying insert the core quickly. is this presta or schraeder you’re using?

Never had a problem with presta valves. Not sure how this would work with schrader. I think you can get an adapter to stick on the end of the pipe that will push the valve in and open it. Might be worth getting one of these. (or hack a bit off the end of an old pump and use that.)

+1 for finger over the end and shove the core in (presta)

+2 on keep the air in there with a finger and quickly put the valve core in before the tyre deflates.

Blinkin Ada!
How to make a simple job complicated…