.. Opening the toilet door in the basement

You got paged into the kitchen and helped him to prepare the dinner? Great!

Oh, yes. Bob must be hiding the key somewhere. Have you searched his room now that he is away from there?

Try to find something suspicious in Bob's room. ( Bob really doesn't look like a person that would use toilet brush. )

Look at the water puddle beneath the toilet brush. After that you can grab the toilet brush. You get a key into the toilet next door.