Access Panel Through Two Walls

Hello - I'm a newbie to DIY Home Improvement, so please bear with me. I need to cut an access panel through two walls in order to reach through one side of the wall to the other side where my washer/dryer sits. I need to do this so that I can appropriately connect my dryer hose from the dryer to the outlet. I plan on installing a plastic access panel, such as this (Access Doors & Panels | Flush Access Doors | Plastic Access Door - 8 x 8 | B204666 - GlobalIndustrial.com (http://www.globalindustrial.com/p/building-materials/access-doors-and-panels/flush-access-doors/plastic-access-door-8-x-8?infoParam.campaignId=T9F&gclid=CKKPqZqL08ECFZM1aQodwyoAVA&gclsrc=aw.ds)). I understand how one cuts and installs an access panel through one sheet of drywall, and I will first install the plastic access door through drywall sheet #1. For drywall sheet #2 (the wall immediately adjacent to the washer dryer), I assume I will do the same except I would be installing the access door on inside of the drywall (rather than the outside as for sheet #1). Any tips? My guess is that there will be both plumbing and wiring between the drywall sheets, given the washer dryer. I assume I should shut off electricity first?