-
Are you using the official Bonty tubeless valve...
Nah, wheel didn't come with one so I used one I'd bought from Cycle Clinic.
I suspect the air was getting around the wrinkled and stretched rim strip, through the spoke holes into the cavity and the valve hole was the easiest place for it to escape.
Triton have a rim strip I hope will work so probably going to order that and see how I get on.
M_V-
I don't have any Bonty rims, but I have some old Light Bicycle 'Bontyesque' rims which use the Bontrager plastic rim strips. If they're the ones I'm thinking of, the only possible leakage point is the valve hole as rather than tape it's a moulded plastic rim strip which curls up around the rim beads. If the tyre's seated against the plastic rim tape, there really shouldn't be any way for the sealant to escape other than the valve hole.
Brommers
Are you using the official Bonty tubeless valve with the woefully-inadequate O-ring seal? If so, bin it, and use a standard tubeless value. The rim strip idea is a good one, the use of a waffer-thin O-ring to seal the valve is a crap one. The Hope tubeless valves work well with Bonty rim strips in my experience.
Leaving sealant to work past the valve is a bad idea, I've found. I've had a couple of alloy nipples give up the ghost due to corrosion from the ammonia-laden sealent.