Save yourself some cash -- find some Fullers Earth on eBay- a couple of hundred grams will do a couple of seasons. cheap as chips. Sprinkle onto some washing-up liquid & mix it up to a paste. that's loads of sinkant for a couple of quid.
I just make small quantities at a time (say about a film canister's worth or about the same quantity as a bottle of Xink!) & store it in an airtight jar, and then fill up a small plastic syringe (with nozzle trimmed back to widen it) and that's a brilliant way to dispense a very small amount of sinkant easily with one hand while fishing.
cheers
iain