This Nauta tank was installed ventless, in 1992. (I noticed the date). Long before I owned the boat.

I did install a holding tank bladder in a previous boat, and installed the included vent. When I reconfigured the plumbing a few years back on this boat, I just left the tank as is. I'll more than likely replace it with something larger and hopefully solid construction, before I start cutting more holes in it.

I doubt you could rupture one of these thick Nauta tanks with your head pump, I think the hand pump would start blowing back(at least you'd realize, something was wrong). It's real easy to keep track of below a lifting hamper next to the head. I keep an eye on it's level, always,..., all holding tanks scare me.

I'm notorious for letting sleeping dogs lie, and I don't smoke.