Songfacts®:

• This song takes place in a strip club and is about anal sex, hence "Back Door." Like "Pictures Of Lily," it was an effort to push the limits of what could be inserted lyrically in a song that receives airplay. It did surprisingly well, charting at #61 in the US and getting substantial airplay on rock radio.
• The Perfect Strangers album features the Mark II lineup of Ian Gillan, Ritchie Blackmore, Roger Glover, Ian Paice and Jon Lord. It was the first Deep Purple album with this lineup since their 1973 effort Who Do We Think We Are.
  
  In re-forming this permutation of the band, they froze out David Coverdale, who was with them from 1973-1976. According to Ian Paice, Coverdale was not happy about it, but understood the decision. Paice said the Mark II lineup was the only one he would have re-formed with. >>

  Suggestion credit:
  Mark - Londonderry, NH, for above 2