No more milk, just the water for liquids. Defo take to the vets.

As for litter, get some clumping stuff, that way you just hook out the solid bits (the pee makes a solid lump) and occassionally top up. A litter tray should be 2-3inches deep in litter. if there's a Pets at Home near you, pick up some of the Cats Best Oko Plus. It's like wood pellets. Clean the tray and put a nice thick amount down. About 3/4 of the bag. Everyday, scoop out the solids, they can be flushed, and every few days sprinkle some new stuff in. Then about every 10 days you can get rid of all the litter, and replace starting again. When you scoop out everyday, if the lid is covered in a lot of poop, you could wash this so the litter tray remains pretty clean. Obviously, with the runs you may need to empty out a little more often the full contents and wash the tray well (with bleach) but this is a small price to get your kitten well again.

Worming, jabs, defleaing and neutering will set you back about £100+ in the first 6 months of their life.

Good Luck.