What´s te meaning of
Less preferably ? and cotton-plugged blow-out type pipet ?
Less preferably means "here is an option that is not as desirable."
A pipette is a chemistry instrument, like a glass straw, designed to extract a tiny amount of liquid from one container and inject it into another. Sometimes they are graduated with a single black line so you can get an exact quantity, e.g. 10 ml or 100 ml. Most use a rubber squeezer to suck and release the liquid, but some actually allow you to use your lips and personally suck. These are usually stopped with cotton to limit the chances of ingesting your liquid. This is the kind you mention. Some people spell it 'pipet' as, I believe, do the Yanks.