It's called Sludge, it comes from South Africa and it is designed to do what all products with that style of name do, which is to sit inside a tyre or inner tube waiting to seal any hole as soon as it is made.
What makes it different from other similar fluids is its claimed suitability for high-pressure tubes with Presta valves. It is, as the box says, 'a tube sealant for the roadies'. Nice.
Application, which RCUK will be investigating soon, is the usual injection through the valve. This is the clever bit. The sealant is formulated to go through the small orifice of a Presta valve without clogging it up. For some reason, probably to stop the toggle nut from sticking to the thread, this part of the valve must be greased prior to application. Otherwise it is the usual gig of filling the tube, inflating and riding in the sure knowledge that you probably won't get a flat.
The stuff is designed to stay in place for a long time, which is not specified but probably as long as a tyre lasts. It is also claimed to protect against 'leaks', so there should be none of that sinking sensation of finding a flat tyre first thing in the morning, just when it is least needed.
Full fitment instructions are provided on the box, including this vital note: 'An air source is required to re-inflate tyres after installation of Sludge tube sealant.' One 100ml tube will treat two tyres, and costs £7.99. A 200ml 'mtb' bottle is available for £9.99. Exactly twice the size? The math is even easier than installation… Review coming soon on RCUK
www.velokit.co.uk
www.sludgeproducts.com 
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