Не выливай помоев, не приготовив чистой воды

Do not get rid of a thing that is not very good before you get a better one

Cf: Cast not out /the/ foul water till you bring /in the/ clean (Br.). Cast not out the foul water till you have clean (Am.). Don't throw away old shoes till you've got new ones (Br.). Don't throw away your dirty water until you get clean (Am.). Don't throw away your old shoes before you get new ones (Am.). Don't throw out your dirty water before you get in fresh (Br.)