The recent thread about Foam Guns mentioned the one Toolstation sell at a tenner .I got mine this morning and altho' there are no instructions it presumably works like any other but if anyone has one ( I know one person has) can I ask about the black knob at the back of the gun and what purpose this serves ....there are also two smaller plastic nozzles so these might be useful as well ...they are like cut down versions of the nozzzles used on tubes of sealant but made of softer material.