These are re-usable silicone teats for Pasteur type pipettes, in 1ml, 2ml and 15ml capacity.
The idea of the cotton plug in the glass pipettes we stock is to stop contamination of the teat, so providing the cotton plug is in situ you should not need to wash the teat between uses. In practice we find it is very rarely necessary to clean the teats, but if you do inadvertently get a perfume material on or in one, they can be washed in plenty of ethanol, dried and re-used.
At Pell Wall we find the 2ml size is the most useful, which is why we include one free of charge with every box of glass pipettes we sell.