Here are some pictures of my holding tank vents, I was asked for some pictures and I figured I would just put then on our thread
this is the black tank vent its pex pipe with a screen on the end
this is the pex pipe coming out of the black tank, theres a 1 1/2 adaptor to pex fitting then it tees off up the floor then out the side its a bit hard to see it cause of the low light
this is the extra vent off the black tank tee, it has a shut off valve on it, but I don't seem to need when dumping
and this is the vent off the grey tank, simple set up seems to work great, so far no smells, and if it did I could just add it to the black vent, but I don't think I have to
so far I have had no problems with this set up its been 3 years, and well used, its all pex line and shark bit, easy to install , and no roof holes.