Specific Ventilation Design Help

First post, Hi everybody   Sorry for the length
Just getting started in the hobby, dabbled here and there. I may be running a small grow tent in the near future and have everything figured out except specifically how to get my warm air outside. I'm assembling a ultra secret, stealth type set up in a portion of the attic. Some real James Bond type shit. My area is not in the highest peak of the attic and I won't have anything going July and August so I hope temps are manageable. I have insulated all of my area, cleaned and sealed everything up. Will be diverting some central heat/AC to this small area which will be passively taken into the tent. I want to avoid cutting holes, installing vents on the roof, or doing anything that is rather noticeable. No one will notice a new vent on the roof, I just don't want to leave too many scars on this (rented) house. 
 
6" filter, 400watt air cooled hood, fan, and tubing. Big fan(vortex s-line), small tent(39"x39"x30.5"), low air speeds (hopefully)
 
 
Couple options: 
 
1) Cut vent hole in the wall/roof in an inconspicuous location and blow out. Shortest piping. This gives my the option to stay inside my secret tarped off area. At first glance into the attic, you cant even notice the space because it is tarped off with the same plastic covering all the walls and it appears to be a seamless roofline. I stress again, secrecy is of utmost concern so staying in my secret room is a plus. One house scar, the vent.
 
2) Branching out of my area there is the sewer chimney. I've read a little about this but this scares my frankly. The last thing I wanna see is last night's Chipotle blowing backwards out of the toilet bowl. I think I would blow throw the roof vent, and put the special crap-tastrophy preventing valve on the sewer end. This requires the medium length of ducting but the most conspicuous to someone in the attic. Also, chimney is 4". Probably would not leave a scar
 
3) A little further, and buried in some walls lies the unused chimney. I could make my way through the walls, chisel a few bricks, and install a 6" elbow blowing my hot breath up the chimney. Slightly longer than 2 but less obvious in the attic. The other side of the walls this chimney is buried in is my bedroom. 8 feet from my bed where enemy spies will likely infiltrate. Noise? bricks can eventually be replace, holes in walls fixed,  buried back in the insulation in the back of the attic.
 
Im leaning towards just putting a roof vent. I intend to build a box to house the fan and double as a muffler with some acoustic insulation. If someone was standing on the ground, under the vent ~15' up on the roof, would it sound like a dryer vent is constantly running?
 
Thanks for taking the time if you've read this far!

 

Thats what im thinking. I just don't want to be out back and be able to hear it. My fan is 350 CFM and the recommendation for my space is ~150 so I will be running it low. 
 
1 is easy, 3 is harder but would be unnoticeable from the outside. I think ill just end up cutting a hole in the roof. My only concern is when I leave, I leave a hole in the roof and/or an empty vent. I could go out the wall but that's more of an area where people will semi-frequently walk by. 
 
I guess option 4 is run it all the way across the attic and put it out the other wall where no one ever goes without a lawn mower. Longest ducting but my fan could push that and I think the long, straight, insulated pipe would help reduce some sound.
 
Ducting lengths: 
1) ~<5 feet
2) ~10 feet
3) ~15 feet
4) ~>20 feet

 

Thank you. Roof vent it is. Any recommendations for what to do after? Just leave it in there plugged up?

 

Attic is about 30-35 feet long in the shape of an L. The short end of the L is where I occupied. A triangular (the roofs peak) area 10 feet wide, 6 feet deep, and a ceiling height of 45 inches or so. Can just barely squeeze the 39x39x30 tent. With the poly all buttoned up, it looks like just a straight 35 foot attic space. I would SCROG 4 plants. 
 
I could vent into the other part of the attic, but its not too well ventilated, and I heard it could be bad to pump warm, moist air into the attic.
 
Im not even going to attempt July and August and its not the highest part of the house so i'm hoping to avoid the heat. My area is on the same level as my bedroom with a separate attic above my room. Part crawl space, part attic, part secret garden...