Chica ok here you are, I think they're more accurate when done in the 1st tri, although after I did them my SIL, cousin, friend and a colleage did them, they were all in 3rd tri and knew what they were having (1 other boy, 2 girls) and they were right for them too, and as you say it's a good lighthearted way to pass the time.
Baking soda test: this YouTube video explains it better than I can
Basically you put a teaspoon of baking soda (I used Dr Oetker) into a cup and then add some of your wee into the cup. If it froths/foams up like the head of a pink of guiness would, it's a boy. If it does nothing and juts goes a bit cloudy but you can still see the separate layers of wee and baking soda when you look through the side of the glass, it's a girl.
Red cabbage test:
You roughly chop up half a red cabbage, and add it to a pot of boiling water. Boil it for ten minutes, strain, then allow the water to cool. Put the red cabbage water in a cup, then add the same amount of your wee. If the colour changes to a reddish/crimson/pinky purple, it's a boy but if it stay the deep bluey indigo-y/violet purple it's a girl. Again it's easier to tell when you look through the side of the cup.
With both of them you're looking for a reaction, if you get a reaction it's a boy, if nothing happens it's a girl. DH did tests with his wee too, just so that we could see what a "boy" result should look like. My results were very similar to his, although a bit less dramatic! I should also add that I used disposable plastic cups!!! 
I wouldn't swear by it, but it's good fun, DH loved doing it!