Settling Basin

In my house built around 1950 there is a catch basin where only the laundry and kitchen sink drain to. The other fixtures drain directly to the sewer without going thru any basin. It is my understanding that this catch basin purpose was to settle some of the phosphates present in detergents, back when the phosphate content in detergents was high, before going to the sewer system. Does anyone know or is able to verify this? Also, what maintenance is required for such basin? Should they be removed or cleaned? There is some solid material in it but it appears to be working fine as far as flow goes. Is there an indication on how to identify potential problems with the basin?

Thanks for your help,
TJerry

Basically a grease trap and yes it is there to catch the bad stuff before it enters the rest of the system. Keep the ingoing and outgoing openings clear and suck the muck out of the bottom so that solids don't float straight across into the outlet.