Hi,
I've just come back from mine today, I drank a pint and half of water at 11.30 (nothing before) - I had to pee at 12.30 as could barely move was so uncomfortable. When went in for scan at 1.00, nurse mentioned how full my bladder still was and asked me to go and have a wee as couldn't get a clear pic.
Think next time I will just have half a pint or something. Guess we all must be different though and either way they can get you to have a quick wee or have a glass of water if needed.
Goodluck for tomorrow xx