It is rarely practical to prepare sauces to order from poached meats, because the liquid is usually so diluted that too much last-minute reduction is required to make a flavorful sauce. Usually integral sauces for poached meats are prepared from the poaching liquid used the day before. In any case, meats are usually poached in advance; pot au feu, blanquettes, and potées are not last-minute affairs.
Poached meats should be reheated in the same way as stews and braises are: gently, in a covered pan, with a little stock.