nettle tea in a poly pin

Hi all.  Just been given an empty poly pin (firmish plastic bag with a tap opening) that I hope to use to make nettle tea in.  Have soaked it for over 24 hours and can't get all the grime off the insides.  I'm just wondering if this matters.  It had contained real ale several months ago and I'm hoping the grime is just left over bacteria.  Would this damage the plants or reduce the benefits of the nettle tea at all?

if it's yeast residue you might get nettle beer...

my dad used to take the Heysham ferry around the war and told me that many of the shops sold nettle beer... never tried it though Hugh FW made some and they raved about it...