When it comes to synonyms for the word "sewage-disposal tank," there are a few different options. One common phrase is "septic tank," which is essentially the same thing but may be used more frequently in certain regions or industries. Another possible phrase is "wastewater tank," which encompasses a broader scope of liquid waste (rather than just sewage) but can also be used to refer to the same type of tank. Additionally, "cesspool" is another word that can be used to refer to a similar type of waste containment system, although this term is slightly more old-fashioned and may not be used as frequently today.