I am having mri with evoist (gadolinium based)how long do i need to drink lots of water to flush it out of my system? is it 2 to 3 days or something?

Eovist: has a dual elimination pathway, with approx. 50% eliminated from the body via the kidneys, and 50% via the hepatic biliary system. If you do not have impaired liver/kidney function, you don't need to specifically do anything and it will be essentially eliminated from your body in a day or so. If you hydrate more, renal clearance will be quicker.