Newb here and have some questions

I have had two pop-ups and a homemade camper but just bought a 09 skyline nomad. My first self contained travel trailer. Got a pretty good deal at an insurance auction because of some water damage but nothing i don't think I can handle. But as with most things that are totaled everyone thinks they need to keep the owners manual and all paper work. grrrrrrr!!

I noticed when I first got it I pluged it into my shops 110 with an adapter ( assuming that was ok) and noticed that the lights were really dim and the more I turned on the brighter the bulbs got and when I ran the slide out out or in they got really bright. I found out the battery was dead and when I put another one In it doesn't do it as bad. Why is that? Does all power go through the inverter? Also after a few days my new battery was dead again. All the lights were off but what else could have been draining it and is it normal to have to keep disconnecting it when not in use?

Also my last pop-up had a toilet with a cassette or what ever so this is my first dealing with all the tanks and such. What are some tips and pointers on the waste tank use? When you empty it how do you clean it out? It didn't come with any hoses so is there anything inpitcular to look for in that or should I just go to my local camper dealer and buy what he recommends?

Thanks for any help and I am sure I will have lots more questions. Lol.