Sup nerds (jokes)

I have a shit load of yard waste mostly gravel and shitty soil and rebar that I need to get rid of. The local waste disposal place weighs my truck before and after I toss my shit but the last time I went there I paid like $50 for just a bit of stuff. I think they're jewing me or their scales are fucked.

I want to pay less so I was thinking how I can do this. Is there some kind of negative weight I can add to my truck and then take it off before the weigh out when I leave? Or can I hang a couple plates from the bottom of my truck and then put them in the truck bed before weighing out?

Help me nerds lol