Welcome from Arizona. You have found the best forum for Montana's there is. I own a 2015 3582RL and know it pretty well. The black and bath tanks are directly under the connivence center. Bath tank first then black tank going across the rig. So bath on the street side and black on the curb side. Both have 3" valves both connected by a single U shaped pipe with the drain pipe exiting from the center of the U. I hope you can visualize this? I wrote it and I am not sure I can
. Do not let anyone cut into the material covering the bottom of the rig. There are lots of wiring and hydraulic hoses lying on it. Tech did that to mine and cut the hydraulic hose to my road side mid and rear rams, a $1,100.00 dollar fix
I have done lots of work insulating between the basement and the belly of the rig. Plus all the outside walls inside the cabinets. Added water filter and a water softener because of the very hard water here on the west cost.
Almost all of what I know has come from the GREAT people on this forum.
But to be fair they have cost me lots of work and money because of all the upgrades they show on here.
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Feel free to ask any question and for sure someone will know how to fix it or how to get it fixed.
But first check the tires and read the strings re tires.
Ok have a great time with your new rig.
Wayne