Tahaarat

Maaul musta'mal

Q:

  1. What is the ruling with regards to water in a bath tub. The moment one steps into a bath tub, is the water considered as maaul musta'mal, thus ghusl will not be valid with such water! Is this correct? 
  2. Is it true that water should not be able to seep through ones mozas? Is it correct?
  3. What is maaul musta'mal?

I would appreciate 5 references to each answer.