Lexs400

Can anyone please post a picture of the 93 LS400 brake booster and it's vacuum hose connections. I'm thinking that the low/spongy brake pedal could be caused by a vacuum leak. How can the vacuum leak be diagnosed and how does one find out if there is a leak to begin with. is there a test that I can do myself ? and If it's taken to the mech, what do they do to test it out ?
Ever brake booster apparently has a vacuum check valve, why is it that when I call the lexus parts dept and ask for the part number of the vacuum check valve they are dumbfounded ?
anyone with info on this ?