how does the fryer oil filter machine work?
Without knowing which make and model you're using, I can only give a general answer.  I worked at a restaurant a couple of decades ago that had a fryer filter machine that looked (and worked) a lot like an old-style canister vacuum cleaner.  Someone on the closing shift would use it to vacuum the oil out of the fryers every night.  The machine contained a filter to strain out debris and a heating element to keep the oil from solidifying during the night.  Then someone on the morning shift would pump the oil back into the fryers, which was a simple matter of flipping the direction switch and turning the pump on.

There are other styles of oil filter machines available, and some of them aren't meant for overnight storage.  One type, for example, looks like a large pan with a filter screen on one half and a pump on the other.  This type is placed under the fryer so the oil can be drained from the fryer's spout into the pan.  Once it's empty, the oil is then pumped back into the fryer.