I almost NEVER weigh myself in the evening unless it is just out of curiosity. When I have, I have been 2-3 pounds heavier than when I weigh in the morning. So no, I don't think that is a reliable weight to go by.
I weigh myself in the morning after I have used the restroom 2 or 3 times and before I eat or drink anything for breakfast. LOL- I drink a ton of tea during the day so it really builds up overnight.
I would suggest buying a cheap digital scale. I bought 3 different scales with all the bells and whistles- not cheap ones, and was not happy with the way they worked. They were very inaccurate. I could step on and it would say one weight, step back on and it would give me another. I finally bought a very cheap, no thrills model and it has worked wonderfully and seems to be very accurate.
I just don't know of any way to accurately weigh yourself in the evening when you have been drinking and eating all day. Also I have heard that you weigh more after working out too. Something to do with your muscles retaining water?? Don't know if that is true or not but that is what I have heard.