Well, I think the obvious thing to do BEFORE you start cutting the hole is to drain, rinse, bleach, drain, rinse, rinse, rinse, rinse to make sure you got all the fun stuff out of there before you drill your hole and have any interesting smells to contend with. Probably couldn't hurt to leave a lil bleach in there after you do the final rinse before you start cutting.
The Tornado goes high enough up in the tank that having some bleach left won't get in the way when you're drilling.
bumpy's right...the kit version comes with a backflow prevention device. Another way I eliminated the problem was to cable tie the hose as it comes off the tank up to the frame. Between the hose being angled up, the backflow preventer and the cap on the hose connection end, I've never noticed any infiltration into the hose on either of mine.
Don
DW
3 Cats
2008 FunFinder X 210WBS
2008 Jeep Hemi Commander Limited