Hope someone can help me here...In my wood burner I have a back boiler that is starting to kettle and hiss. Normally I would think about adding some additives to the header tank, but when I went to screwfix they have some superconcentrate- which apparently can be added to the backboiler directly. It looks like a tube of sealant. They sell a cheap adaptor kit, which I bought. Any body used these before are they better, do I just pump it through the drain c*ck- want it all just squirt out?/block the drain c*ck ? Do I use the whole tube- Any advise /web pages to use Thanks.