youll need to tune your A string down so that its 7th fret matches your open G string.
is the tuning mark used on his 2 string slide bass.
[ Tab from: https://www.guitartabs.cc/tabs/m/morphine/whisper_btab.html ]
---------------------------------------------------| (every other time
-0--03b-00-2-2-5-2-3-3-6-6-6-6-6-6\----------------| it slides up to the
---------------------------------------------------| 9th fret instead of
---------------------------------------------------| sliding out)
dont worry im not lookin at you....
-------------------------------|
-0~~~~~~~~~~~~-----------------|
-7~~~~~~~~~~~~-----------------|
-------------------------------|
whisper me your number, ill call you up at home