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Inflate and as soon as it starts hissing tighten it, you can always tighten a bit more when all the pressure is pushing it. If this doesn't work go with the sealant or if it's leaking a lot you may have done a too big cut in the tape, replace and be careful with the valve hole.
Also going for a little ride used to work for me with leaky tires, somehow helps the sealant to go in the right places.
Success. Soapy water and smashing the hell out of a track pump and my GKs clunked into place. Glugged some Stans in and not a leak to be heard.
However, I'm struggling to get more than 40psi in them as the valve (I think it's a Stans one) hisses like fuck, no sealant coming out but it won't seem to take more than that. I only want to get it to around 50-55