several ways to do it
1 ,have another number added to ring in on your line you have now ,and thats called a destinktive ring or ringmaster service ,it will ring different than main line and the fax will answer only that ring
2 have a switch in front of all phones and when it (someones fax)
rings your house it routes it to only the fax machine this is easy !
if its a voice call it rings your phone if you don't answer it goes to your machine .
3 some people have voice mail at home and if a fax comes in it records it for later transfer to your house fax or it records voice you on most of these can send the fax anywhere to a hotel or office or home ps first it rings you home phone 4 or5 times then goes to voice mail if you don't answer COOL