A quick question about CWE, dosage and tolerance.

[DaveRave]

Dear SWIY,

SWIM and a friend of his have stumbled upon 150 prescriptioned co-codamol tablets (each 8mg Codeine/450mg Paracetamol) and have decided to acknowledge the high-potential.

SWIM has tried codeine before, using 60mg a few weeks ago and 180mg a few days ago (althought with what I have been reading here, 90mg was actually wasted due to enzymes being taken up by the first 3-pill dose).
His friend has never used Codeine before.

SWIM is also in posession of all the necessary apparatus for CWE.

So, SWIM's question is simply this:
How many tablets should SWIM and his friend use in their CWE?
And, if known, what volume of water should be used?

Many thanks for your help.