pull out the plunger, pack it in, use a large enough nozzle st it doesn't require large amounts of pressure, replace plunger.
can be a variety of viscosities, but the two extremes (liquid or solid) are bad. usually something tacky, sort of like freshly mixed 2-part epoxy is nice and holds stuff down quite well.
probably personal preference, but I don't like pastes that aren't really pastey.