Act Responsibly. Think Safety First.
The military may ask you to lay your life on the line at times. A number of us here at Avanti are prior military. But risking your life waterproofing in a confined space is just silly and avoidable. Did you know that in a low oxygen environment, people will act normally at first, but will then abruptly feel dizzy and black out in a matter of seconds?
So whether it's a tank or a manhole, you need to think safety first. Get certified to enter a confined space. Classes are cheap, easy, fast, and can even be done over the internet. Sniffers and gas detectors are a must. A tripod and hardness system is more than a good idea, especially since many municipalities are removing ladder rungs from their manholes. Personal protective equipment (PPE) like gloves and safety glasses may not be fashionable, but should never be overlooked.
Be safe out there!