Sam Lutfi -- the self-proclaimed manager of Britney Spears who is suing her for defamation -- claims in new legal docs a drug-sniffing dog found a cache of crystal meth in her home.
The allegations were filed in connection with the upcoming trial. Lutfi claims Britney, along with her parents Lynn and Jamie -- defamed him by saying he drugged the singer during her dark period.
In the docs, Lutfi talks about what he would want Britney to testify about. As of now, she will not take the stand because a judge has found she is not competent to testify as a result of the conservatorship.
Lutfi says in the docs Britney should testify about an incident in 2007 ... he claims he "brought drug-sniffing dogs into her home ... and they found a cache of crystal methedrine, which was destroyed."
Lutfi goes on ... "Britney should further testify that drug dogs found 'hot spots of drug residue in the carpeting, where her young sons [ages 1 and 3] played during visits."
Lutfi says he covered it up by shampooing and eventually replacing the carpet.
Lutfi also claims Britney told him her dad Jamie "was a violent racist," and an abusive alcoholic.
For the record ... Jamie became Britney's conservator and is widely credited with saving her life.
Britney's reps could not immediately be reached for comment.